Its in the same realm of "People who can fight, don't need to fight"

If a fat lonely virgin says that "I choose to be single". It has no meaning, cause its not like he has women flocking over him. If a successful playboy who gets women anytime he wants say it, then it has meaning.

Similarly, most "good guys" or "nice guys" are only that way because they have no choice. Its the only strategy available to them to get attention.

So what happens when the "nice guy" needs to defend his woman from a "bad guy"? You think he's going to stand up to him? No, most of the time they cower and run. So much so, its biologically ingrained in women to detect this.

To be able to fight bad guys, your man must be able to be bad as well. That's why its an attractive quality.