Going straight to the point. I am one of those players who choose to play Ahri or Diana as a "support". Here are a few things i would like to inform open minded players:
1) Doing so is not equal to trolling. If i wanted to troll, my choice of champion would be irrelevant.
2) Don't flame or rage because its a weird pick. Yes it lacks many aspects that other characters (casual supports) cover, but offers other possibilities.
3) Losing a game while playing said weird character does not mean the character is trash in this position. Just like you can lose games with any support, so you can with these.
4) Blaming the loss of the game on this weird pick is nothing more than turning me into a scapegoat for all the things that went wrong in the game. You focus in this one aspect of our team and completely overlook the mistakes the rest of the team has made. Yes it could be exclusively MY fault, but many times its not. Refusing to adapt to a different character's kit is not MY problem. If you play Varus for example against Braum and Lucian and i have Ahri, its not irrational to just stay under the tower and farm there. Yes, you will lose a bunch of cs, but you will lose LESS than you would if you actively tried to move out in the open. It's simple calculus. A bit of cs + exp vs no cs, no exp and enemy kills. It doesn't matter if i made a mistake to pick a certain champion against the enemy's combo, but it matters if you refuse to acknowledge reality and adapt to it, ITS YOUR FAULT.
That's all. In case anyone cares, my mentality going in games with these picks is the easy initiation and considerable burst they can provide, against which most supports don't have time to fart, let alone protect the adc and turn the tables. Plus, its easier to gank other lanes as well and make the jungler's job easier.