Now, about Modern Orthodoxy...

Charedi rabbonim who have openly proclaimed the 'Modern Orthodox' movement to be a no longer acceptable, if not patently non-Orthodox movement, here (the article itself, and here additional insight here;), I'm aware of other public leaders' statements, but will have to hunt them up later), bother to specifically single it out as a movement. Think about it. If it was mitzvah violation as such that offended them (or that they thought to be errant, not simply distasteful), there would be no reason to condemn an identity.

The "identity" common to Jews is "Israel" - and all klal Israel are ultimately - to some degree, however minor - selectively Observant - that's what Tshuvah, Viduy, Tachanun, Yomim Noraim, etc., are "for", right?...

...but those who do not identify as 'generally observant' are considered inadvertant/unknowing/unwillful transgressors, and regarded with compassion and outreach, etc, etc; actual derision and scorn is reserved for those identify with or through Modern Orthodoxy. Just as the Orthodox have long ago dispensed with considering the Conservative movement to be halachic (which remains debatable, so long as Conservative Judaism claims to adhere to "pluralism" - as many within the movement see no basis for saying C.J. denies Observance as a legitimate derech for Conservative Jews...), many Charedim, leaders among them, are quite willing to declare the same of Modern Orthodoxy. The words of the Charedi Rabbonim noted above were public - and clearly, the attitude has developed and been 'worked on' outside the written, published setting, as many 'closet' Modern Orthodox can attest (having mixed in 'charedi settings'). Many Charedi laypeople are well on their way in this regard; open public dismissal in settings from Shabbat tables to yeshivah halls, has been too frequent for me to even specify instances of.

Much antagonism also arises in the Charedi Kiruv sphere about Modern Orthodoxy - I know this by experience in kiruv settings, by reading literature and attending 'lay-Outreach' campaigns. Yet Modern Orthodoxy, since it's earliest days and among its antecedents (Hirschian Derech, etc) - has always been resoundingly Kiruv oriented...the shuls are totally open to whomever may want to come, aliyot are given without recourse to tsitsit-checking, etc....the movement has always been about inclusiveness, non-judgmentalism and the 'relevance' of Torah lifeways to modern life, and to a degree there has been 'dumbing down' or 'accomodating' (within halachic limits), Yahadut to fit the comforts of those being reached out to, etc...

...all things also indicative of Charedi Kiruv efforts.

but among the Charedim....they become condemnations leveled at Modern Orthodoxy - clear symptoms of its degradation, at best, illegitimacy from infancy at worst (and "most likely").
When Modern Orthodoxy succeeds in their kiruv efforts - drawing the not-yet-Observant into their pews, their classes, their kehilot and schools, brings them closer to Observance - they are deemed, as a movement, villainous. When charedi kiruv settings draw the not-yet-Observant into their pews, their classes, their kehilot and schools, brings them closer to Observance - though many are not fully-compliant with even general observance....it's a wonderous - nay, miraculous success - they are heroes...

On other dynamics between Modern Orthodoxy and Charedi Judaism, I highly suggest the Yuter piece that this post is excerpted from. I don't take his tack, personally. Similarly pertinent is this recent post, where response is made to an equivocation of certain Charedim and the Essene sect.