If someone at work was writing blog posts with white-supremacist code, then yes, I would probably go to HR and they would probably get in trouble. Maybe they wouldn't be fired, but they would be placed on another team. And then the people on that team would find the blog posts, and the same thing would happen, and they would probably be let go at some point.
Because people that do that type of thing usually cannot shut up about it.
I think you should read DHHs recent non-technical blog posts (highlights like "As I remember London") and make your own mind up about that. Me and a lot of other people on the internet want nothing to do with it.
Noam Chomsky: 'If we don't believe in freedom of expression for people we despise, we don't believe in it at all.'
Also, your solution doesn't solve your problem: your colleague won't stop to hold ideas that you don't like, nor his blog will disappear. If it's just a blog, he didn't harmed anybody, whereas you got him fired.
There's multiple levels of freedom of expression. You could argue, and people do, that the company has it's own right to freedom of expression, and wants to portray itself in the way it wants, and that necessarily involves deciding who they work with.
For example, if I told you that you are forced to associate yourself publicly with someone you don't like and don't want to associate with, then you might say I'm hindering your freedom of expression.
And this is missing the elephant in the room: white supremacy is fundamentally anti-free-expression. That's one of it's core tenants. So we have a little bit of tolerance paradox here.
If we allow those who oppose free expression to freely express that, then they express it by limiting free expression, then by allowing free expression we've actually suppressed free expression. So, it's tricky.
In case of a blog, it's separated from the professional life. The colleague can just behave normally and avoid political topics.
It's normal to hinder freedom of speech, up to a certain level in the context of the company: I would not like to be teached about Marxism-Leninism by the barista making my coffee.
It also allows people to separate professional and private life, just line sexuality: if you like latex parties, you can enjoy them without having to tell everyone or coming at work wearing latex. It allows collaborators of different sensibilities to work together. Your supremacist colleague may even then work with non-white people and find them nice and competent!
Last, you are projecting ideas: I'm sure that many white supremacists are pro-free speech, having experienced censorship. You clearly aren't.
Because people that do that type of thing usually cannot shut up about it.