https://www.bloomberg.com/news/articles/2018-03-21/youtube-b...
Perhaps you will say that "instructions on how to assemble firearms" is not an expression of a political view, however I would argue that preventing people from imparting legal factual information to help other people exercise a constitutional right seems like something that, if the government were to do it, would be a breach of their First Amendment rights.
So as not to be seen to be taking a specific view on "gun rights", let me give a different (hypothetical, and non-equivalent) situation to clarify what we mean by "banned for political views alone" here.
Suppose that Google had different politics and decided to ban channels that provided assistance to women seeking an abortion. Perhaps Google would allow channels to advocate, in the abstract, for "abortion rights", but not to give any practical advice on how to exercise them. I think that most people would agree that this would count as unconstitutional "viewpoint discrimination" if the government were to do it, so it is effectively a "ban for political views/expression" if Google do it as a private corporation.
I can't speak for the people that create these channels or want to make these expressions, but I have to assume that at least some of them think that they are making people safer by teaching them how to legally arm themselves. That seems to be a view that Google disagrees with, so they have implemented an editorial policy on YouTube which prevents people from expressing that view in a meaningful way.
Perhaps you think that Google would only be banning people for their political views if the company openly said to them: "We are banning your channel because of a political view you have, even if you never express that view in any of your videos." That seems like an unreasonably high bar to require though. If Google said "You can support any party you want, but we won't allow Democrat political candidates to put their campaign ads on their channel." then that would, at least to me, be a ban on political views.