If people are using Marcuse's ideas, they shouldn't be making cartoons with Popper. The ideas are very different.

The problem with Marcuse is that he overstates the problem and comes up with a solution that's worse than the disease even if the disease is as bad as he thinks (and it's not).

You don't need a level playing field to have truth discovered through rational discussion. You just need to have some baseline respect for truth, some intellectually safe spaces for discussion to take place, and not so great a power disparity that the vaguest whims of those in power completely obliterate any considerations of truth.

And we have that, for the most part, in most of the Westernized world.

This includes the right to protest and engage in civil unrest, when things are very unjust and serious, and powers that be aren't taking you seriously. If there was any doubt before, post free-speech movement (evidenced most strongly in the U.S., but the sentiments spread throughout the Westernized world) made this absolutely clear.

As you point out, violent counterbalance to fascism generally doesn't produce a superior outcome. If the violent counterbalancers win, you get authoritarian leftism (c.f. communism), which has almost as awful a human rights record as fascism. If they lose, the fascists have a mandate for their totalitarianism. Indeed, if it hadn't been for revolutionary Marxism (which Hitler railed against extensively in Mein Kampf, for example), the Nazi party likely wouldn't have gained sufficient traction to exist.

The solution to fascism isn't particularly difficult, I don't think: transparency, open dialog, and an unwillingness to bend to fear or allow the tools of fear to spread. Fascism is almost impossible to justify as a form of government, and it's bad for most people, and pretty transparently so at this point, so as long as you get it into the open, it can't take hold.

You have a system of laws to protect people from actual harm and imminent violence, and enforce them, so you can't spread fear through violence, or doxxing (threat of violence) or anything like that, to "win" despite minimal support.

The moral panic on the left that equates the floating of fascist ideas with a fascist takeover (or insensitivity with violence) actually encourages fascism, because once you start responding to the panic, a unified society and openness goes out the window, everyone has to align into camps, and the most strident and aggressive one wins.

Having a system of government where the most strident and aggressive are in charge is bad news.