Can you elaborate on what you're trying to say here, or how it relates to this article?
If you believe a significant chunk of the voting population is swayed by YouTube comments in their political beliefs, you could just as well be arguing for forcibly sterilizing the feebleminded.
There are other potential problems than swaying voters, though: swaying non-voters (to keep them uninvolved) and swaying potential future voters (such as teenagers).
To the extent that people engage in any format, propaganda in that format is concerning. And like it or not, people do engage in YouTube comments.
If you think that being smart and vigilant is enough to protect yourself from this type of manipulation, I think you're wrong. I find it very easy to fall for social proof in internet comments, and I've been in the tech industry for over 10 years. This has nothing to do with intelligence.
It's not just YouTube. Twitter and the rest are vulnerable to the same problem. The whole idea of humans socializing on the internet is vulnerable to this.