How are unusual thesis topics looked at?
For a topic like this, I’d recommend making sure it’s something you’re comfortable having your identity tied to.
On this particular topic, I know folks who have outwardly countercultural identities built up, in which they've made work in this area part of said identity, and others for which they are more mainstream, matter-of-fact about the role of sexuality in everyday lives.
The key thing to avoid would be a topic that made you personally feel awkward/embarrassed about telling people about it (unless you were sure that you wanted to become less embarrassed about it, and practiced braking down your discomfort before becoming committed to it).
With respect to careers, it will likely be limiting in some aspects, but open other doors (and this ties into the identity aspect via asking yourself what you actually want out of life).