Since there seems to be some confusion on this point: in canon, at least, an "Unbreakable" Vow didn't actually stop you breaking it, it just killed you if you did. If a person is willing to sacrifice their life - and if you resurrect using a horcrux, that could easily be worth it - you can still commit crimes.

And if you swore to obey the law - is being found guilty is now an automatic death sentence, even if you honestly thought it was legal? I doubt a working legal system based on Unbreakable Vows is trivial to come up with.

That said, they are unquestionably broken in canon. Very, very broken. Few are willing to stake their life over, say, business deals, but there are loads of situations in which they would be a massive game-breaker.