I haven’t read the original context, so some copy-pasta would be helpful to figure out what the full argument was.
But the first off-the-cuff reaction in my head-- The alternative for a woman who had no husband was most likely to starve to death. And her children would starve as well. So, you could make a heroic sacrifice and preserve your honor or your chastity— and die, and condemn those dependent on you to death as well. Or, you could be compelled by circumstances to sacrifice your honor and your chastity, and do that, which made it an involuntary sin, because you were doing it not because you liked the work, but because you didn’t want your kids to die.
Nowadays, that’s not the case.
It’s a bit similar to the thing in Matthew, where Jesus said–
But I tell you that anyone who divorces his wife, except for sexual immorality, makes her the victim of adultery, and anyone who marries a divorced woman commits adultery.
So the woman in the situation is forced to commit adultery by the men in her life-- because the alternative is death to herself and her dependents. So the burden isn’t on her; the burden is on those who set up those voluntary circumstances. In the case of a widow, whose husband isn’t taking care of the family because he’s dead, it’s a set of involuntary circumstances.