you do not 'trespass' because it is an abandoned house and the 'Vigilant of Stendarr' at first glance is a good guy because his intention is to fight the evil haunting the house which is a danger to the citizens of Markarth. just let it go.
If I met up with some random dude outside of your house and stormed inside killing everyone inside because I disagreed with your religious views, even though you haven't actually done anything to hurt anybody, that would be "good"?
Abandoned means owned by you? Obviously it isn't "unoccupied" or else how could he suspect people are worshiping their gods in there?
Clearly it's occupied by somebody. And what is that person doing wrong? Why do they deserve to die? Because they have a religious view different than you or the Vigilant of Stendarr? How are they a danger to the citizens of Markarth? Have they killed/hurt/harmed somebody? Have they barged into someone's home to persecute/kill them for their religion? Maybe it's you that is a danger to the citizens of Markarth.
