Just for fun here, let's explore the notion that it's "safer" to be a lesbian. I guess in the limited sense of "safer sex" you do have certain advantages like not getting accidentally pregnant and being at less risk of getting an STI. So there's that. On the other hand, there's the phenomenon where you try to simply tell a therapist about your sexual orientation and they scramble to find a way to frame it as a pathological adaptation to childhood abuse. That feels not so safe to me. Also there's that way in which young lesbians get kicked out of their homophobic parents' homes sometimes when their sexual orientation is discovered. Not safe either. Then there's job, housing and healthcare discrimination. Not feeling safe there. Also if you care about stuff like basic legal protections for your family and marriage/partnership you're frankly still SOL in most of the US and the rest of the world. All in all it strikes me as the kind of thing you wouldn't just do for convenience. Finally, lesbian relationships sadly are no healthier, easier or less likely to become abusive than straight ones. So to me, your T's hypothesis is pretty freakin' flimsy.