While I admit that there is a lot of trash on youtube (such is the nature of things when you provide an open platform for anybody to upload virtually anything they want), there are a lot of decent quality videos probably in all genres.
My two year old loves to watch educational videos in both English and Hungarian, Hungarian being the one that specifically interests me since that is much more difficult for me to find through other venues here in the states. I have also used it for visual aid when working on repairing circuit boards, modding consoles, etc. Most recently I used it to watch a quick unboxing of a Rudolph themed train since I wanted to put it back into its original box after christmas and the way they package things requires a PHD in engineering lol.
Anyway, my point is, there absolutely it quality content on youtube, but you probably won;t find it if you just search trending or popular videos (same as you probably won't find many quality news articles suggested to you on facebook). Of course, you can spend the time susbcribing to the proper networks so that other (likely) quality feeds come to your attention.
Anyway, this is longer than I intended it to be. My point was, no everything on YouTube is crap and some of it is actually worth watching in the highest quality possible.