I guess my issue is specifically with 'break things' as it overgeneralises the idea of experimentation (which is something I do agree with). The impression that 'move fast, break things' leaves me with is that it's ok to break anything and that it's also (implicitly) not a big deal if they stay broken or somehow hurt a user (e.g by exposing, even temporarily, what was once private).

Even though it's a wonderfully pithy 4 words, people can interpret them in many different ways, most of which I'd argue are not good for the end-user.

"... you are already writing software which you implicitly acknowledge can go wrong. Software has bugs!"

Agreed, but shouldn't the intent be to create things in a way that tries to reduce the likelihood of damage while still allowing plenty of room for experimentation? i.e take some care that what you're about to do/push isn't going to do harm? If I follow the 'break things' mantra, I don't need to care. That's what bothers me. It's so easy to hide behind when something goes wrong.