Oh indeed. If your main reason to want to be professor is that you want to teach some classes and publish some papers then there are definitely options to do that via working in industry (depending of course a lot on your field). However if you actually want to be a professor and work full time within the university world, with all the pros and cons that brings, then it's very hard to do without a doctorate.

But I absolutely agree if you 'just' want to be involved with some research projects, publish a bit on the side and perhaps teach a few courses then there are many ways to reach that goal that don't involve becoming a professor.