Users are also part of the content-generation algorithm. Youtube uses my view history in their recommendation algorithm to others. YT uses my interactions the same way, whether it's engaging with the creator in the comments or providing feedback for other viewers or just simply giving it a like.

Yes, I'm consuming the service, but I'm also contributing to it. Less users = less engagement, and maybe that's good for YT's bottom line but it's harmful to the ecosystem.

Using words like 'theft' to describe visiting an openly-accessible webpage with a browser extension that modifies the presentation of that webpage is a bit extreme.