Depends on what these thoughts are. You should mainly remain vigilant not to cross this unspoken vague boundary between fantasy and reality. Guilt should be something to put you back in place after you ride over that limit. A personal example being fapping to a cartel execution of a woman with huge tits by beheading her and wishing they would leave her tits and cunt exposed. Half way through fapping, i was like "wtf are you doing mate, this is real shit" so i managed to refrain from it. After i jacked off to something imaginary, and got a clear head i realized how much guilt would have fucked me up if i had actually nutted on this poor woman's execution.
Stay.Damn.Vigilant.