Of course, the answer for that is for HN to bite the bullet and actually integrate a relational database, if only to improve performance and scalability.
And as far as lobste.rs goes, the culture there seems to be more restrictive due to being invite only, and having a policy of banning not only offending users, but the users who invited them, and the users who invited them, as far up the (publicly viewable) graph as deemed necessary. This inevitably leads to far more posts than comments, and less diversity of thought or critical discussion, by design. Nevertheless, using tags doesn't seem to have interfered with any of that, so it shouldn't necessarily interfere with Hacker News' culture either.
HN, however, has open membership, and any tag system employed here would need to take the heterogenous nature of the community into account. Since politics is one of the more divisive topics here, a politics tag would probably be inevitable. Lobste.rs would just not allow anyone they consider too political to join in the first place.
As for lobste.rs, a website I didn't know existed before your comment, looking at the frontpage I see that the "politics" tag is conspicuously absent, and instead all tags are about rather objective things like technologies being used (with maybe the exception of a lone "philosophy" tag).
I'd also point out that if I had up all the number of comments of all the stories on the front page currently I end up at a whopping 42 comments with most stories having none. I'm sure it's a very nice community but it's really too small to use as a reference.