I think you might be going easy on Heilemann in suggesting that he didn’t know about Halperin because they traveled in different social circles because Heilemann is gay. Having watched him for many years, I don’t sense that Heilemann, who is married to a woman, is gay.
And even if Heilemann were gay, surely over the course of a decade he would have heard rumors, etc., about Halperin’s misbehavior.
I believe Heilemann’s double standard is more likely attributable to the fact that it suits his political agenda to condemn Moore, whereas if he had admitted he knew about Halperin, he would have been criticized for having worked with him for so long.
Of course, Heileman had to know. Maybe he's next on the hit parade.