Whatever the din is or is not,let me quote a gemara with meforshim:
1 shita: mamzerim after 3 generations will be "butl".
2 shita: after 10 generations.
With in that tgere are two shitas
1: butl means they will die out.
2: butl means they will be considered regular ppl, because once something is "listed" in a category in this world it is too in the one above ( note that all this is talking about that no one knows that they're mamzerim for 3/10 gen.)
Another totally different shita holds that once mashiach comes all ppl with defects will be healed, and says a mamzer Is a person with a defect so they will be "healed".
So im not upset.
Nor do I belive they did something asur (besides for chillul of THE NAME).