Great question.
I don't think it's necessarily a bad thing, but I do think we should strive towards only having single asserts in our tests. This means you write a lot more tests and our tests would end up testing only one thing at a time.
Having said that, I would say maybe half of my tests actually only have 1one assert. I think it only becomes a code (test?) smell when you have about 5five or more asserts in your test.