Those blogs sound awful. Breaking things down methodically is one thing, but blatant trash-talking helps nothing and no one. Happily, you recognize the negative impact now. A sign of growth, like lovely literary flower~

My fortune cookie take is that there's a time and a place for things, even Mary Sues. Your time may not match up with others', and vice versa, and that is just a part of art and life. I love seeing threads on Tumblr and wherever that defend "cringe" like Mary Sues, because they are important.