I think the primary divide is this: liberalism is an ameliorationist mindset and leftism is a perfectionist one. Sometimes it feels like leftists looked at the "and yet you participate in society" comic guy and thought "his underlying point has some merit; wouldn't it be great if society had no problems and I could therefore participate in it without complicity" whereas liberals think "yeah that laborer could have a better life and we should build structures to get them there, ignore the troll."
The animating drives of leftism and liberalism differ then as well. Where leftism seeks a just society and pursues justice as its highest goal, liberalism seeks to push towards the conditions for human flourishing. The New Liberals see markets as an incredibly powerful force for enabling that flourishing, which is perhaps where your historical perspective comes in, and want government to set up those markets in a way that is efficient at raising living standards and allowing people to better their lives (this thru-line drives their strongest policy positions: abundant housing, free trade, and unrestricted mobility [whether thru immigration or occupational licensing reform]). Unfortunately this animating love for the surpluses created by markets leaves them a little flat footed on social issues (while you certainly could frame repro rights as the protection of a market for reproductive care it would be deeply strange to do so) and sometimes at a bit of a loss where government created market failures aren't as glaring as they are in housing. I was really struck by the nods to the ways that high childcare costs impede families from growing and flourishing and place great financial stress on them in the vulnerable pre-public school years, but the most concrete policy solution seemed to be one that would get derisive jeers were it proposed on housing: just subsidize demand. But because high child care costs do discourage prospective parents from having kids, discourage young parents from having more kids, and place great strain on family budgets, it's obvious as a pressing barrier to American families reaching their greatest potential, and so liberalism (New or otherwise) feels obligated to find a way to assist.
I found myself examining these tensions at play within myself in the discussion of means-testing tuition grants at community colleges. From the liberal perspective it's obvious how you get there: some kids are prevented from reaching their potential in the workforce by not being able to afford community college, these kids largely come from households making less than 100k a year (since those above that line can presumably already afford the nominal tuition costs at community colleges), so our subsidies should be efficiently targeted at students being held back by our current structure. I see the logic in that, but progressivism has influenced me to see the absurdities there: if a community college education is minimally necessary to enter the workforce, surely we should provide it to everyone, just like we do high school education. The justice framework seeks equal access for all and frames this sort of education as a right. Additionally, the abundance of means testing, both in government provided services and through the tax code, means that middle income families often face marginal tax rates approaching or sometimes exceeding 100% (this one sort of violates the conditions for human flourishing and the justice principles, because being able to better one's conditions is part of human flourishing, but I find the justice aspect more salient [though avoiding the income tracking people have to do and the suffering caused by losing benefits if they do it wrong is a strong motivator that fits into both categories]).
These thoughts might not be your preferred flavor or solve your dilemmas on whether to wade into discourse at house parties, but I think there really is a positive vision to be staked out beyond the merely historio-empirical and grounding desires for policies that might seem niche, globalist, or (god-forbid) libertarian in the vision of a somewhat improved society might help sell them to our leftist friends who also strive for an empathy-driven ideal of a better world.
I think the primary divide is this: liberalism is an ameliorationist mindset and leftism is a perfectionist one. Sometimes it feels like leftists looked at the "and yet you participate in society" comic guy and thought "his underlying point has some merit; wouldn't it be great if society had no problems and I could therefore participate in it without complicity" whereas liberals think "yeah that laborer could have a better life and we should build structures to get them there, ignore the troll."
The animating drives of leftism and liberalism differ then as well. Where leftism seeks a just society and pursues justice as its highest goal, liberalism seeks to push towards the conditions for human flourishing. The New Liberals see markets as an incredibly powerful force for enabling that flourishing, which is perhaps where your historical perspective comes in, and want government to set up those markets in a way that is efficient at raising living standards and allowing people to better their lives (this thru-line drives their strongest policy positions: abundant housing, free trade, and unrestricted mobility [whether thru immigration or occupational licensing reform]). Unfortunately this animating love for the surpluses created by markets leaves them a little flat footed on social issues (while you certainly could frame repro rights as the protection of a market for reproductive care it would be deeply strange to do so) and sometimes at a bit of a loss where government created market failures aren't as glaring as they are in housing. I was really struck by the nods to the ways that high childcare costs impede families from growing and flourishing and place great financial stress on them in the vulnerable pre-public school years, but the most concrete policy solution seemed to be one that would get derisive jeers were it proposed on housing: just subsidize demand. But because high child care costs do discourage prospective parents from having kids, discourage young parents from having more kids, and place great strain on family budgets, it's obvious as a pressing barrier to American families reaching their greatest potential, and so liberalism (New or otherwise) feels obligated to find a way to assist.
I found myself examining these tensions at play within myself in the discussion of means-testing tuition grants at community colleges. From the liberal perspective it's obvious how you get there: some kids are prevented from reaching their potential in the workforce by not being able to afford community college, these kids largely come from households making less than 100k a year (since those above that line can presumably already afford the nominal tuition costs at community colleges), so our subsidies should be efficiently targeted at students being held back by our current structure. I see the logic in that, but progressivism has influenced me to see the absurdities there: if a community college education is minimally necessary to enter the workforce, surely we should provide it to everyone, just like we do high school education. The justice framework seeks equal access for all and frames this sort of education as a right. Additionally, the abundance of means testing, both in government provided services and through the tax code, means that middle income families often face marginal tax rates approaching or sometimes exceeding 100% (this one sort of violates the conditions for human flourishing and the justice principles, because being able to better one's conditions is part of human flourishing, but I find the justice aspect more salient [though avoiding the income tracking people have to do and the suffering caused by losing benefits if they do it wrong is a strong motivator that fits into both categories]).
These thoughts might not be your preferred flavor or solve your dilemmas on whether to wade into discourse at house parties, but I think there really is a positive vision to be staked out beyond the merely historio-empirical and grounding desires for policies that might seem niche, globalist, or (god-forbid) libertarian in the vision of a somewhat improved society might help sell them to our leftist friends who also strive for an empathy-driven ideal of a better world.