Perhaps it's simply a case of semantics here, but there's a huge difference between assertive and aggressive, especially in reference to sexually oriented activity.
My take is as follows: An assertive lady is not likely to "take one for the team" if she's really not into it. She's circumspect about it, explaining her lack of interest to her mate privately, not by being rude to the person in question. When involved in activity, she's going to be sure she receives as well as gives pleasure. She will certainly clearly communicate if "a line" is being crossed and put a halt to it. She knows what brings her pleasure, and will convey it to a partner in a clear, not necessarily verbal, manner. She will not be coaxed into something against her wishes, and
will be verbal in that regard if warranted.
An aggressive lady may foist attention upon an unsuspecting prey, even going so far as to pursue when it is clear the object of her quest is uncomfortable. I heard an aggressive female at one club proclaiming she had recently acquired a dandy new strap on and she fully intended to use it on every man who she thought were "too full of themselves."

I myself had a lady slid herself under the stall door in the ladies room at a club to have me "to herself".

I thought that was beyond aggressive - it was pushy and rude and just plain scarey. We did actually some time later become friends, but it took me quite a while to be able to get past that first experience of her behavior.
I don't think there's anything wrong with assertive behavior, in fact I think it is quite attractive and desirable. You know where you stand, and aren't playing covert games. But I can also understand the need to soften that with a bit of charming flirtatiousness as well. It's just more friendly in the social environment of lifestyle encounters.
There are always going to be those men who will refer to an assertive woman as a "ball-buster" for not going along with anything and everything he may wish. And those really extreme fellows who will deem a female as "lesbian" if she's not interested in him. Those sorts are not likely to missed if they're never on your dance card.
WR