I can say yes, but not no?

In Cardiff, it seems, posters have started to appear saying "Don't vote".  They are aimed at Muslims, and their premise is that "none have the right to legislate except Allah" and that therefore voting offends against the tenets of  Islam.  The council have said they will remove them - why??  The fact that I - and I imagine most people - do not agree with the sentiments being expressed is really neither here nor there.  If I can put up a poster saying "Vote for Joe Bloggs", then why not a poster saying "Don't vote at all"?  Unless there is something in election law that I am unaware of, I can't see the distinction.  Just because I - or you - disapprove of something, doesn't mean it shouldn't be allowed to happen.