I'm mad about autofill for one main reason
I've played since s2 and back before new champ select was implemented into dynamic queue, we all remember what that was like. We were much more prepared to be forced to support, because let's be honest, if you were bottom pick and not a support main, you likely would be forced to support. You'd say the role(s) you preferred and it'd be a toss up whether or not you got that role. I rarely got forced to do anything other than support, jungle being the 2nd most forced role on me (but that's okay for me, it's my secondary role).
So I am used to the idea of having to play a role I'm not accustomed to. But the reason autofill frustrates me is because for a year, I haven't touched the support role - I haven't needed to. I'd always get my role and I think this actually drastically improved gameplay too because everyone was getting roles they were best at. But now, a year later, I am being forced to play a role im completely out of touch with. I can refocus on it and frankly, support would probably be my 3rd most preferred role. But the fact I've been told I don't have to worry about that for the last year and in the last few months, I suddenly have to, going from playing my two best roles to this feels like I've been robbed. And that's frustrating because I really liked only having to play two roles.
The other, less obvious issue is people have become more entitled to roles and refuse to communicate or share roles. Auto filled players throw tantrums and players who got their roles get upset when they're being held hostage to surrender their roles (it has happened a few times in my games already). At least under the old system, you knew ultimately pick order was law. But with this, as I've said, people are so entitled now they'll throw fits when they don't get the roles they selected (and I can't blame their frustration).
It's just made champ select really toxic again and despite how unpopular ranked/dynamic queue was this past season, the one plus to me was that champ select seemed significantly less toxic.
And make no mistake, I understand auto fills purpose and while I'm inclined to disagree, I can understand why someone would see it as the lesser of two evils in very high rated games because it kills excessively long queue times. But if still feels like complete shit when it happens to you. Can we get something? Like, if I get autofilled, can I get bonus LP for winning an autofill game? Nothing crazy, maybe a bonus 5 LP. But something that takes the sting away from being forced to a role I have to beg to be carried in because I'm inadequate at it..