There's an important feature somewhat obscured in the answer that should be drawn out, viz., that merely because Plato disagrees with his interlocutors does not make them straw men.
While I agree that some of Plato's Socratic interlocutors are straw men, whether they are straw men or not does not hinge on whether he includes voices that disagree nor even on whether their views are absurd. I think among the interlocutors we can distinguish roughly three categories:
- useful idiots
- genuinely different views
- straw men
"Useful idiots" are those views that exist to help us see an obvious reply to an obvious objection. Thus, they say something we might first think when we hear an idea. And this gives Socrates the chance to explain how that does not apply to the view he is trying to articulate. This sort of dialectical method is also central to Hegel where the negative is necessary to move forward because it highlights what is wrong with the currently held view.
I do think there are some genuinely different views voiced at points during the Republic, Parmenides, and also the Laws and several of the later dialogues. There are questions raised where Socrates does not win or at least where as a reader we are not compelled to agree.
There are still some straw men of course. But I don't think Plato is our worst offender on that point. And what makes them strawmen is if they articulate views that someone genuinely holds in a way that does not do justice to that view.
So for instance in contemporary philosophy, not every objection I include in a paper is one that I really expect someone to raise. Instead, some are to dispel misunderstandings before they happen. Often the best way to avoid this is to quote, but there's really not much lying around for Plato to quote. It's not clear how much access he would have had to texts or how much beyond a cursory familiarity his school would have had with some of the sophists.