I attempted to register
crack.house. I was told that I could not (by namecheap), because "the domain name contains a trademark".
How often does this happen, and is there anything I can do about it?
Yes. They are right.
You do not want to register a trademark as a domain name. One can argue locale in some respects, however, this is a company that offers...
Printing fonts that can be downloaded provided by means of electronic transmission
...which means that locale does not come into play. They will always have a claim against your domain name registration.
This is not something you want to get into. It could mean a Federal lawsuit which always means at least $10k to begin defending even when you roll over and say "I give." Otherwise, you would at least lose your domain name even if they do not make a claim in court. It is a big risk that I advise against.
If you don’t operate in the exact same market segment as the trademark holder, then use another domain registrar to register the name that you want. The only way to violate the trademark would be if, for example, they sell cars and you sell cars.
It might be that every single word in the English dictionary now has a trademark applied to it somewhere in the world. But again, those trademarks only restrict a direct competitor in each particular market segment.