The obvious implication is that we're dealing with sampling bias rather than the entire species being xenophilic perverts and this is actually a roundabout form of attack.
Imagine you're in charge of an interstellar civilization. Multiple colonized planets, even more space habitats, etc. Population in the trillions, minimum. And you want to conquer a planet full of aliens. Now sure, you could go with conventional tactics and almost definitively win since if you have the technology to travel to them, it's a safe bet to assume you drastically technologically outgun them, but you don't have to.
Considering the sheer size of your population, despite being a minuscule percentage of the total, the number of xenophilic perverts* you've got could very well outnumber the aliens you want to conquer.
So put an ad on your imperial equivalent of the internet asking for volunteers, then drop them on the alien planet.
They'll have happy, hedonistic relationships with the locals, which, on account of sharing less DNA similarities than sea cucumbers,
produce no offspring. Because of the large number of individuals of your species peacefully interacting with the locals, they're a viable market, so the locals themselves will build species-specific infrastructure and agriculture for them. Then a generation later, you move your colonists in effectively unopposed.
* Be realistic people. If a UFO was to publicly land and the alien crew emerged in full view of the cameras of eyewitnesses, how long after the first pictures hit the internet would it take for the first rule 34 to be created? This goes doubly if they come out deathrays blazing.