I think people need to stop using being submissive as a coping mechanism when they have low self esteem or mental health issues. You won't find anyone whose low self worth has been 'cured' by being degraded, beaten, etc. As you said it's basically just another form of self harm, which predatory doms look for and exploit.
But at least you're smart enough to realize this which is a good sign. The 'fantasy' part is a grey area because even though this may just be 'a fantasy' you're still acting out this fantasy with your body, not to mention all the hormones and emotional processes which ARE real and happening, and even more pronounced in women. So it's not really 'just a fantasy' when all these very real physical and biological events are happening.
Safe, consensual, but people always forget about the SANE part. There are already enough submissive, vulnerable women with low self esteem that men exploit. Please don't enable any more creeps. It might feel good in the moment but if you're feeling terrible afterwards, it's a sign something is wrong. Listen to what your body/mind is telling you.