A phobia is an irrational fear. In the wake of regular worldwide terrorist attacks in the name of numerous interpretations of Islam, it's hard to see how concerns about Islam and political power are any sort of "phobia." But let's accept for a moment that it can be possible to be unfairly concerned about a particular Muslim, even so.
That still leaves two questions:
1) At what point does a concern become valid? Vox defends Ellison against charges arising from his association with worse characters, especially Louis Farrakhan. What we have learned about radicalization indicates that much less close contact than this is necessary for it, though. Perhaps it's not fair to hold Ellison to blame for his associations, but there has to be a point at which it would be fair. At what point would it become fair? That's a question I'd like to have answered.
2) If we're to be excessively careful not to criticize individual Muslims for associations with others who may be more radical than they, why doesn't this point apply -- say -- to Hindus? Consider Tulsi Gabbard. Isn't she being treated exactly the same way, by the left, that they're concerned that Ellison is being treated by the right?
What's the difference? Gabbard is a Hindu, and she knows lots of other Hindus (and Indian Americans) who have inherited or developed concerns about Islam and/or Muslims. Ellison is a Muslim, and he knows lots of other Muslims (and African Americans) who have inherited or developed concerns about Judaism and/or Jews. These seem like parallel cases to me. So why promote Ellison to the leadership of the DNC, and run down Gabbard?
I suppose you could reverse the polarity on that question, and ask me why I'm more inclined to defend Gabbard. But I know why: because she's an Iraq War veteran. She's earned a space for considering her unpopular opinions, whatever they are. I don't have to agree with her every time to know we're on the same side when it counts. Ellison offers no such evidence of service that would counteract his associations.