I can't imagine doing any sort of BDSM play without a safeword or some sort of non-verbal way of signaling "enough". Whether a rope is suddenly too tight or the sub's headspace has gone somewhere uncomfortable, at the end of the day the "slave" and "master" are still people getting each other off in a particular, agreed-upon way, and people should have a right to be able to ensure their comfort and safety, EVEN WITHIN the context of a scenario where 'comfort' and 'safety' are ostensibly exactly what you're trying to escape.

I agree that there should be no conditions placed upon use of a safeword, and that this guy the OP is talking about should look for a different domme. I'm sure there are people that get off on not having a safeword, but if this guy is expressing doubts, he's not one of them, and he deserves to play with people that agree with his style of play.