The issue is the delegitimizing impacts of the appearance of impropriety. A referee's ability to do his job is fully contingent on at least some degree of acceptance that calls are being made legitimately and objectively. Obviously, that is a legitimacy which has been already corroded in the last few years with the shambolic state of PL reffing. A referee then plainly saying that he hates a specific club and calling their coach a German
? It brings the whole thing into a higher degree of disrepute.
Regardless of whether there's a clear and direct impact of Coote hating Liverpool on Liverpool's results (something which, due to sample sizes, would be basically impossible to sketch out anyway), he will
never be able to be accepted again as an impartial referee, which is what the whole system is predicated upon. And it creates a higher level of open season for his peers, who are all going to be looked at through the lens of "what's in their coked-out video?"
It deepens the legitimacy crisis to a pretty significant degree - whether or not he specifically f***ed over Liverpool is absolutely beside the point.