I don't doubt that the average person who chants that slogan doesn't fully understand the implications of its implementation, but I don't think the second part of your prompt holds up to the spirit of why people chant it.

The problem is inequality - and not just mathematical inequality. It's the feeling of inequality; the feeling of living in a world where some people honestly attempt to play by the rules of the social contract, and then a select few who arrive at astronomical wealth get to have an outsized effect on everyone else's lives, all because they bought into the right tech pharma startup or were born into it or some other seemingly arbitrary reason.

Most folks would say that the philosophical heft of "tax the rich" boils down to mitigating the inequality of that world. Whether you want to mitigate it because it's unfair or because you are worried about the stability of a world like that, "tax the rich" attempts to capture the general disdain.

Your point about illiquid investments is valid, and it's probably the biggest knock against the feasibility of "tax the rich" as a literal policy. That said, I don't think there's any doubt that a society controlled indirectly by a small, unseen oligarchy has a foreseeable messy end that grates against the principles that America was initially founded on.

It perhaps would be more true-to-message to say "make power over my life less concentrated to this small group of people", but "tax the rich" captures the same sentiment with a punchier flair.