Well, I might be wrong, but isn't there supposed to be a separation of church and state (SCS) in most of Europe? Seems like the lawyers of our demonstrator will have a pretty strong case:

(a) Either scientology is a 'real' religion, in which case you might wonder if it is acceptable that a police officer in function is so emotionally involved in Scientology that he feels insulted by the use of the word 'cult'. That's a violation of SCS, which is in most non-dictatorships a pretty basic constitutional principle.

(b) Or Scientology is not a real religion and the SCS is not applicable here. In that case, demonstrator guy is right: every religious group not accepted by mainstream society is per definition a cult (see source of all wisdom; also in OED).