“What is so wrong with her regretting what was done to her?”
Well, if you see the scene in question, what people really are objecting to is that she characterizes herself as a “monster” because she is infertile, as if it is equivalent to Banner being the Hulk. There are probably a couple different ways to interpret the dialogue there, but it is a pretty strange and awkward scene.
I think that when she refers to herself as a monster, she is referring to what the KGB has turned her into, not that she is infertile.
She does not characterize herself as a monster because she was sterilized but because she was trained to be an assassin and has killed hundreds if not thousands of people in that capacity. That is reason why she joined SHEILD, to try to make up for the monstrous things she had done as an assassin. This is the defining motivation of the character in all the films she has been in (and in the comics), and that anyone can miss what is so patently obvious explains why reality TV is so popular.