It's impossible to know without watching something whether it's full of swearing or homophobic / misogynistic / transphobic hate speech.
Ads are not targeted to the actual viewer, but to some combination of regular browser user and main youtube user. this means that children will be shown ads for alcohol or gambling. (note this goes against what Youtube says here about complying with local law: https://support.google.com/adwordspolicy/answer/6012382?hl=e... Note that this is something all ad networks get wrong, and it's likely they're going to see regulation in the uk at some point if they don't fix it.)
It's hard to know before clicking a link whether it's sponsored content or not. (in the UK sponsored videos need to be clearly identifiable before the user clicks the link or clicks play. in the US sponsored content needs to be clearly identified).
If two people (eg a parent and their child) watch Youtube the recommendations fail hard. If a single person watches youtube the recommendations are pretty poor.
Assume someone making $50k lives in not NYC, I imagine this scenario could be a lot better.
For a more extreme version of MMM, read http://earlyretirementextreme.com/. This guy (Jacob, who MMM mentioned in this interview) never earned much money (never over $50k prior to becoming financially independent), and retired after working 5 years. With a little creativity, most people can retire far sooner than standard retirement age.
Assuming a $50k income post-tax