The conversation I'd like to have with the typical progressive:
Progressive: I'd like to see poor people acquire food, shelter, health care and education.
Me: So would I.
Progressive: Wonderful! Here's the way I think we should do it, and which I currently think is the best way.
Me: Alright. Here are my disagreements, and here is what I think is currently the best way.
Progressive: Alright. Here are my disagreements, and here are my responses to your disagreements. Do you see any fault with these?
Me: Here are the faults that I see, if any, and my disagreements and responses to your disagreements. Do you see any fault with these?
And so on, and so on.
Here's what I tend to actually get:
Progressive: We should pass policy X to give poor people food, shelter, health care, and education.
Me: I do not think that is the best policy, we should consider alternatives, like this.
Progressive: I hate your idea and it will never work, largely because it's not my plan. Why do you oppose poor people having food, shelter, health care and education?
Me: I don't oppose that, but I do not think your policy is the best route to those goals.
Progressive: By criticizing my plan you are making it harder to enact it, which is tantamount to an attack on the poor. Why do you hate the poor, especially women and minorities?
Me: Your policies are idiotic, and also go fuck yourself.
And so on, and so on.
I'm not going to say every conversation that goes south is due entirely to the person I'm talking with. I can snap at people, and if someone snaps at me, my natural response is to escalate it. But that first line - that key difference - is something I run into again and again.
For too many people, "a plan to achieve a given goal" is identical to "desiring to reach that same goal" - such that if you disagree with the plan, you're actually disagreeing with the goal. If you oppose state-run health care, it is for some people literally impossible that you would even desire to see poor people receive health care. Impossible! And if you insist otherwise - if you discuss the ways you wish this would in fact come about - it's mentally written off as insincere. It has to be! Because the alternative - that someone can have broadly good moral goals and yet stand in opposition to the progressive plan - is an alien thought for many progressives.
I do not think this is fundamental to progressive thought - it's not as if desiring state-run health care turns you into a person like this. I think it's a function of political influence which our lives are typically inundated with. Likewise, I do not think this sort of thought is absent on the conservative side - it's very easy to find people who equate 'opposing the GOP' with 'opposing gun rights and the free market and also you're an atheist communist'. But generally - not always, but generally - a conservative will recognize me as having common ground with me, so if I disagree with them I can at least get the benefit of the doubt and the conversation will continue instead of my getting an accusation of outright betrayal.