Calling Trump a sex pest is a personal attacks, but well-grounded in his actual behaviour

I disagree, it's inflammatory, based on some sketchy evidence, and has absolutely nothing to do with his ability to govern. So there's absolutely no reason to make that argument.

People should be concerned about Trump and the MAGA movement

Oh, I absolutely agree people should be worried, but if they're going to call them fascist, they need some really compelling evidence. And in almost every case, that evidence just doesn't exist. The stronger the accusation, the stronger your evidence needs to be.

I don't call them fascist because I don't have the evidence for that, even assuming Jan 6 was intentionally sparked by former Pres. Trump. The furthest I'll go is to say he's anti-democratic (he attacked the election with zero success) and that his policies would be harmful (high tariffs cause inflation, unfunded tax cuts cause inflation, etc). I then speculate about possible motivations (Trump is a narcissist, wants to benefit himself and other rich people, etc), and indicate that the average person will be worse off because of his policies. If you attack the person directly, you'll put them on the defensive (you're being unfair, or whatever). If you attack the policies and demonstrate that they help some group the listener/reader doesn't like (say, billionaires) at their expense, you might convince them to consider alternatives.

If you believe his presidency would push us toward fascism, show the evidence. And then indicate what your preferred alternative (I assume Harris?) would do differently. If you can communicate that succinctly and in simple words, you could actually change peoples' opinions. If you come off as calling names (i.e. sex pest fascist), you'll just put people on the defensive. Don't attack the individual, attack the ideas that individual espouses, and show how those ideas will benefit others you don't like at your expense.