Are you sure it's not because... "he suggested Trudeau is a Muslim convert."... ie. he's a nutty lie-sayer ?
I haven't seen any evidence that Fatah himself is saying Trudeau is a secret Muslim convert. I did find this Twitter post where he asserts that a lot of people in Pakistan seem to think that's the case, however:
https://twitter.com/tarekfatah/status/693077333301944322?lang=enPakistani truck drivers turning their rigs into rolling shrines to the Canadian PM... that's hilarious!
As far as "promoting the Quebec mosque conspiracy theory", it appears that is based on Fatah repeating the claim that the second man detained by police that night, Mohamed Belkadir, was an accomplice. Given the circumstances under which Belkadir was taken into police custody, that's an easy leap to make. As there was a lot of misinformation being spread that night, I suspect Fatah made an honest mistake.
Why do I give Fatah the benefit of the doubt? Because he has a long track record of being reasonable and respected:
In December 2008, the Toronto Star suggested that Prime Minister Stephen Harper appoint Fatah to one of the vacant seats in the Canadian Senate.[22] Toronto Star's senior editor Bob Hepburn wrote that Fatah is "A prominent spokesperson for secular and progressive Muslim issues who would bring a much-needed unique perspective to the Senate."
-k