"You shouldn't post YouTube links on Mastodon because it's owned by Google!"
Talking like this looks out of touch.
Alright, perhaps ideally, you might not want people to use YouTube, you might want them to use something like Peertube instead, however, it's undeniable that YouTube is a part of everyday life. I don't think berating people for that is helpful.
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There are plenty of things which frustrate people about YouTube, such as arbitrary censorship and downranking. Or that YouTube keeps trying to get you to login. It might be better to talk about those than berating people for linking to the site.
I remember YouTube used to mess with people for... Cursing in a video. I saw a post earlier today complaining about how YouTube apparently doesn't like nudity.