I feel YouTube and more broadly the internet is something that accentuates intelligence. For example, if you are smart you will discern the wheat from the chaff and be able to use the internet as a tool to gain information thus you will appear more intelligent than you are. On the other hand, if you are not smart then you are more likely to fall foul of the misinformation and draw absurd conclusions that make you seem more stupid than you are. YouTube and internet as a whole is a tool; it can be used or abused depending on the way you operate it.

Other things to consider is that YouTube, its algorithms (and this applies for many things in the internet) will show you content that you appear interested in. This leads not only to more extreme views but cultivates an echo-chamber environment. As you are exposed to less contradictory information you become less tolerant of alternative opinions, and this only gets worse if your opinions are reinforced by people in your community leading to the them and us mentality. Overall, the internet can and does lead to more extreme opinions and reduces the scope for actual debate. The politics of the US seem to reflect what is happening on the internet.

I would add a final point and that is of curiosity. When using most mediums, be it TV the internet or whatever most people simply lack the curiosity or the energy to seek out new information, novel ideas. In most instances people use devices not to be educated and informed but to be entertained. There is lots of educational content on TV and the internet but the demand is way higher for products that entertain us. Why is Hollywood, Facebook, Instagram worth billions but educational channels lagging way behind? Demand. At the end of the day people just want to have fun, not think too deeply about anything. They lack the curiosity and societies in general tend to discourage this instinct.