I think that denigrating anyone, Gadol or not, especially in a public forum, is probably a major no-no. Disagreeing with someone’s ideas however, feeling that those thoughts may go too far or are machmir beyond that which Hashem wants of us, is NOT the same as making light of the PERSON. IMO, it is not insulting to a Gadol or even to a “mere” Talmid Chochom (nothing mere about Rav Falk at all), to say that one is not mekabeil his particular mehalach – UNLESS that mehalach is unquestionably 1000% the correct one.
Not all RABBONIM agree with and accept as Torah m’Sinai some of the ideas expressed in Rav Falk’s Sefer. It is therefore not surprising that many people here likewise find some of his words to be hard to hear. Separate the kovod we surely owe him for his extensive Limud Torah, from your feelings (and those of some Choshuveh Rabbonim)that many of the things he wrote are chumros and not halacha l’maiseh.
One may not necessarily agree that everything a great Rov says or writes is always applicable to all of klal Yisroel, but we still must respect the Torah mind that believes enough in these ideals, to want to teach them to us. The only way we can dialogue about these things, is if we retain mutual respect.