Besides content harmful to kids, there's a ton that's harmful to just about any human psyche from a social or personal perspective. I wasn't aware of how bad it was until I recently browsed Youtube.com from an incognito window and saw the default experience- it's rage bait, misinformation, and just straight mental junk food. My logged-in experience is nothing like that, thankfully, but I can't imagine throwing a kid into a fresh YouTube account and them needing to pare that down (or even having the critical thinking skills to do so).