I think it's OK to move fast and break things when you're in the initial product development stage, where you need to develop features quickly and try lots of new stuff to see what sticks. Once you have paying customers though, it may be time to slow down and start caring about stability, at least for your main branch.
It's also ok to "move fast and break things" when the most critical thing you're breaking is your annoying high school "friend"s ability to share the latest racist meme with you. There's a reason facebook made this phrase popular.
