The whole concept of a machine having consensual sex with a human is just stupid.
I tend to imagine the whole deal in the episode as "Data's curiosity" as to what this whole sex business was about.
Someone else said this, and I tend to agree:
Tasha was intoxicated and used Data as a blow up sex doll.
Data was impaired as well, and as a machine, was not able to calculate what was probably going to be not appropriate behaviour.
My understanding of the behind the scenes is that at this point in time, they weren't sure what Data was supposed to be (if he was an organic AI, and whether he was created by aliens, etc etc.) and at this time they hadn't yet come up with the concept that Data does not have feelings and emotions like we do.
The whole idea that a machine could experience sex the way a human being is ludicrous. Even if it were possible (do we really understand what pleasure is, or even pain?) what would be the point in giving a robot this feature?
The whole idea of Data being "fully functional", why? I could accept it as maybe Dr. Soong providing Data with a working electronic phallus (hah hah) so that he could provide functioning sex (although crippled) to a potential mate.
Other than that, there really isn't any use to data for having one. If he wasn't "fully functional" he could just use a strap on and it would do the same job.