Ah, okay.
I know they can be taken back, but I was thinking of looser rules for getting back the baby, like simply approaching it (I mean, surely they would choose their parents over an ugly, derp-snouted hag right?). I was thinking that lonely ladies could become aggressive once the steals a baby to balance the "reclaim by approach", since I think she would be determined to keep it.
Lonely ladies not mating with spiky bodied males is good, but you would then need to watch both your males and females. My main concern would be the domino affect this causes:
LL mates with one of your males
Either steals a nest or an unclaimed one to have the baby
The baby grows up to be either another RM or LL
That's one more rogue to watch out for (or more, since I assume there's more than one lonely lady on the island)
Rinse and repeat for an isle o' rogues
I personally wouldn't want to deal with it, but maybe they could only appear on killer islands (or hard and above?). I think rogue males only appear on medium islands and above, or at least that's what I've noticed. I feel like being bombarded with lonely ladies and rogue males the moment you leave your grassy starter island might be a bit much and frustrating.