Re: Don't black holes accrete mass?
Yes. I commented about that on the original article as well - there's absolutely nothing impossible about this black hole and it's extremely misleading to keep calling it that. However, it is both unlikely and, importantly, never previously observed.
For the former, the important point is that you don't get entire stars simply falling straight into a black hole and disappearing. The process is actually extremely messy and results in huge amounts of material being blasted away rather than falling in - that's why we see very active accretion discs, jets of material and radiation, and so on. So to form at ~10 solar masses and increase up to ~70 doesn't mean eating 60 stars (which would already be a lot), but probably several hundred at minimum. Aside from being unlikely to start with, since pretty much nowhere has that many stars positioned in a way that they'll collide (even dense globular clusters and galactic cores are noted for having a lot of closely packed stars that aren't actually constantly colliding), that sort of thing should leave plenty of evidence behind.
As for the latter, the fact we've never seen it before obviously still doesn't mean it's impossible, but it's always going to raise questions about why we haven't seen any others. New discoveries that also contradict existing theories are always going to suffer under Occam's razor. If theory says something shouldn't exist, and all previous observations agree that it doesn't exist, you need pretty good evidence to support a claim that it actually does. The original guys might turn out to have been right after all, but at this point it seems relatively unlikely.