you make a good point that it's true that there's no 'official' rules in BDSM, it's up to everyone and their partner(s) to decide what it is that's comfortable with them!
ada not having a safeword is supposed to show off the level of complete trust she has in daniel, and to show how committed to the lifestyle she is! so much so that she's willingly 'thrown away the key', so to speak. of course, it's not REALLY the case. it's just not having the safeword just fully completes the fantasy of the master/slave dynamic! if ada was to show genuine distress at her situation, daniel would drop the pretense immediately for her. think of it as a 'nonverbal safeword'.
some people are uncomfortable with the idea, and we understand! its a balance we need to strike to keep the fantasy intact while still respecting the agency of the characters themselves. for ada and daniel, this is something they've built up over a decade of trust with each other, and fully negotiated and consensual. it's something they'd never consider doing with Cindy, considering she's still a novice (at this point in the story).
i think it's just that the negative version of BDSM gets depicted so often in fiction, as
geigi says, that it gives a false impression of real life BDSM as this manipulative abusive process when it's not! so naturally, people are very passionate about the topic!
