This story has really incensed me. Either Pastor Ssempa is incorrigibly stupid or he is calculating and devious in the extreme.
Assuming the latter, what he is trying to do is tap into the disgust that he knows everyone in the congregation will feel from being shown imagery that, quite apart from anything else, is completely inappropriate in a church setting. Regardless of whether or not you attend church, we all know that it is a place where the carnal and material are held in low esteem, especially sex, which is why modesty is so important at a service.
To show porn of ANY kind in a church will automatically cause revulsion in the congregation, simply because it is precisely these kinds of acts that are to being temporarily ignored or assumed not to exist while they are in there.
To show a form of porn that depicts acts that the congregation are almost guaranteed to believe are "unnatural" will only intensify the revulsion. If I were forced to watch gay porn, I would be angry, but I would direct my anger at the tactless jerk who forced me to watch it. But Ssempa is (probably correctly) assuming that the congregation will instead direct their anger towards the people in the video, and by extension all gay people.
So not only is he perpetuating the irrational hatred that is expressed towards a group that is struggling enough as it is to be accepted, but he is unfairly inflicting something on his congregation that they don't want to, and shouldn't have to, have inflicted on them.
And he probably enjoys seeing it more than he lets on.