I think you've made a great point here - but I've seen people explicitly saying they want communism. Look at how often /r/LateStageCapitalism, an explicitly communist subreddit is on the frontpage of reddit.
If people were just pushing for a few more socialized services, I think they've got a good argument to make there. There are good tweaks that can be made. But if they're pushing for a complete change to the system I think they're off their rockers.
The key is what happens to suggestions for "good tweaks". Do they get considered reasonably and implemented fairly? Or are people denounced for even seeking tweaks?
Flexible mixed-economy capitalism seems to be pretty stable. Capitalism that's blind to inequality produces an increasing long tail of disaffected victims with nothing to lose. Hence the rise of kick-over-the-table politics, epitomised by Trump.
At the end of the day, the actual change in the mix of social services might just be tweaks, but you're also talking about a very significant change in worldview.
People are ragging on capitalism because they're looking over the pond to countries that see capitalism as a tool to serve democratic interests rather than as moral worldview, and they kind of like that idea. Interestingly, those countries aren't really less capitalistic (the Heritage Foundation puts the U.S. in the same bucket on their Economic Freedom index as Sweden and Germany), but their culture is less centered around glorifying the capitalist.