Well, I'm the only person I know personally that spends time browsing reddit on his phones (because on a PC videos do not autoplay), and I've installed a different client mostly because it won't autoplay anything.

But I do have a lot of friends that spend time browsing facebook, and not a single one likes autoplaying videos, either wanted or unwanted ones.

Videos do not get into your screen at the same exact time you focus your attention on them. On the occasion that you'll want to watch the video, autoplaying just forces you to see a lot of out of context spoilers and video endings.