Consider the difference between noticing someone you happen to pass on the street and following that person with a video camera every time they are outside. Corporation should not continuously monitor people, even in public spaces.
It's difficult to simply live life and never, ever be in a public space.
No one has to publicly stream on Twitch or other services. If someone wants to broadcast video but do it privately, there are ways to do that.
It might be a small stage for a small streamer, but turning that stream on still means you're getting up on a stage, and you are implicitly accepting that you'll be watched. It's a choice to put yourself out there.
Yes. Related to the difference between “available” and “easily accessible” - a lot of information about e.g. politicians may be freely available, but it usually doesn’t make a difference unless a journalist makes it easily accessible.
I'm aware, I used to watch streams. Some of the comments suggest that publicly broadcast information is fair game for large scale, corporate sponsored data mining. The existence of such data mining has a chilling effect, causing people who may wish to broadcast to avoid it. Example are elsewhere in the thread.