There are no stupid answers, only stupid people.

What I mean by this is that no answer (or opinion) is ever 'stupid' or 'wrong' provided it can be explained or justified. (Obviously I take as axiomatic that justifying opinions is useful and meaningful, and I think I'd find it troublesome to have a conversation with anyone who didn't.)

So a far as that goes, yes, people are entitled to their opinions, and I'm entitled to think their opinions are wrong or stupid if they can't or won't explain them.

I do think that the phrase, "Well, I'm/you're entitled to my opinion" is mostly used in two ways. Firstly, it's often used belligerently by someone who can't or won't justify themselves, but wants to be heard all the same. Secondly, it's often used in a conciliatory way, when an argument has become unproductive or threatens to become violent or abusive - it's the debating equivalent of, "Leave it, Wayne, he's not worth it!"

At least in the second instance, I can see its value - sometimes it's more important, at least in the short term, to keep the peace than to be right.