The real problems are Bieber, dislike bar and hate words. Rated 4 out of 5 stars
This add-on is great but with some extra functionality, it could be absolutely brilliant.
Firstly, MildTinyRock's suggestion is excellent. A filter against racist, homophobic and sexist words would be excellent.
Secondly, a 'Bieber' filter is urgently needed. Virtually every video on YouTube is plagued with annoying irrelevant comments about Justin Bieber.
Thirdly, same again for a 'dislike' filter. The ability to blank out all comments containing the word 'dislike' would be a contribution to world health and happiness.
In summary, a customisable version of this add-on which allowed the user to define the list of words which they never wish to see in YouTube comments would be amazing. I think an anti-Bieber filter alone would earn you world fame and a lot of grateful $5 donations. Please give it some thought.