My humble opinion is that it boils down ego threat. Certainly, there are other factors that weigh-in, but I have never been disquieted enough by this behavior to pause and think it out. Perhaps that is a greater reflection of my own self defense mechanism, but I am unsure.
Precisely it. It's an inadequacy complex.
"Why men think badly of women who love big cock?"
The question itself is the answer. Man strives to preserve himself, as does every other living organism. However, man's case significantly differs in that he has achieved consciousness, therefore his ultimate means of self-preservation is his ego. It is what permits man to possess, or lose, his will to live and by definition, how he defines his worth.
Unfortunately, negativity does not nurture the ego- go figure.
Those of lesser intelligence tend to protect themselves from any form of negativity, criticism in this case, using particular methods. The most common being, criticizing before being criticized. This doesn't necessarily ensure absolute protection, but it 'softens the blow.'
Simply put, criticism isn't as harmful when the critic is someone you don't think very highly of. "I don't care if she doesn't think my cock is big enough, I think badly of her anyways."
Having said that...
"Women who love big cock"
Imagine for a moment, all men had "big cock".
...
Problem solved.
A 'well-endowed' man will never think badly of a woman capable of appreciating (and more?) his glorious endowment.
And the reason why your question is "Why men think badly of women who love big cock?" instead of "Why some men think badly of women who love big cock?" is because studies indicate a majority of men fear their penis sizes are inadequate. Ego.