Having such a family member does not detract from the gedolim,admorim,roshei yeshivos or organizations it only reflects on the indivduals who went off
In the mind of a friendly person. In a noob, passerby or hater, they're only going to remember so much about a topic that doesn't really affect their lives. Usually something they can speak lashon hara about. Also like why stop at the leader and off the derech people then? Why not every Chabad Rabbi, when we mention them we also maybe mention they had a downsyndrome son who wouldn't let you put tefillin after 18? The people that left or never liked it in the first place aren't part of the story of a thing. They're satellite details. You could equally spend that time talking about charity work in your area.
If you want logical consistency, the Gemarra G-d forbid is "whitewashed". The only time they'll mention evil doers like the woman who married the Greek and hit the altar with her shoe, is to educate for important lessons where no positive example is appropriate, and in this case to educate that she was still mad at Hashem for letting the people she sold out to win.
It's not whitewashed to not talk about the dog of one Rabbi and how the dog licked its own butt because there are mostly dogs and most of their activities are less productive and appetizing than that. A respected Chassidic organization will have people that went above and beyond, or even harder, kept everything to an extremely high level, and those are the guys that are the story of the Breslever or Gerrer or whoever. It's true that the fact that the dog of one Rabbi may have licked his own butt more than once does not detract in the mind of anyone that he is great. If you spend your time when talking about a group focused on details like that instead of what the group is good for, for friendly people it's interesting, B"H Chabad didn't go that way, for others it's like, "oh bad thing and them related to bad thing so they must be bad things too".
Anyways plenty of yeshivot I've been to the Rabbi will tell you about other members that were relatives that went off, as a lesson that yichus isn't everything or whatever. For instance, my great great grandfather was a Chassid of the Gerrer Rebbe and his son went off, and it's known but in Gerrer history my story and his story are not relevant unless I go back and become a Gerrer Chassid and then only the details that make the teshuva see all G-d's will story sound pretty.