Are ARAM players toxic?

I got flamed HARD for not being good at a champion I've never played before. Isn't playing with what you get the point of ARAM?

I don't feel compelled to reroll a champion I haven't played, or am not good at. Is it expected that you only play champions you're already good at?

I am wondering if the reroll system just leads to people playing what they like instead of the random champion they get.