Key word there is CAN BE. It's up to developers of said product to release a stable build. The notice is put that there, because it's not a final product and thus, unexpected things can happen, like crashes
I can assure you though that we've extensively tested our build, and crashes have been dealt with.
But, nobody is telling you to play the BETA 3 when it's released, if you don't want to that's fine. But don't complain to us that because it's not final, that your not going to play it because of your own doubts of BETA's. Thats not our problem.