Really should be able to opt out of joining in progress.
I just quit anyway soon as I load in because I like full matches only, so it wastes my time and it keeps the team who are a man down already down for even longer as the entire time I was loading in and then quitting out they could have actually had someone who doesn't mind late joins join instead. Lose-lose.
I'd rather they just give people joining in a late match more bonuses. Like someone above said, joining in progress matches is a necessary evil