Earlier quoted context omitted.
If he's presenting a factual summary of what's going on, his "motivations" are irrelevant. If he's not presenting a factual summary of what's going on, his "motivations" are likewise irrelevant. If you can refute his claims, by all means do so, but vague ad hominems don't impress me.
Not sure why accurately reporting his track record of attacking Wikimedia with a clear - and self admitted - right wing bias is a 'vague ad hominem'.
Either his claims are factual, or they aren't.
If they are not factual, they should be refuted, but appealing to his "motivations" or "track record" is not a refutation. It is an ad hominem attack, i.e., a logical fallacy.