Because people who get filled on role they don't want (Support mostly), often end taking their team hostage by picking a troll pick, inting, greifing, flaming and what else because hey, Riot filled me in a role I don't want. Instead of asking nicely to switch, they find it neccessary to keep 4 person hostage of their poor behaviour.. It really need to be addressed..
your best bet...play with people who want to play support.
the auto fill system has its place, it isn't perfect and obviously has downsides but it has been in the game for some time and most people are accustomed to it by now.
even if you play with someone (that grabs support) you could very well be autofilled to jungle (the second most common role for it) and that can be far worse to be autofilled into
support is much easier than jungle, if you mess up a few times as supp you can easily adapt. but messing up as jungle can often lead to a lost game
