I don’t know the exact context for this reply, but in this particular instance, I guess I do agree that the main drive for sexual immorality and sex crimes is the pleasure that the doers of the disgusting things receive. I don’t know what else would drive them to do that stuff. If we wanted to specify, perhaps it’s both sexual and sadistic pleasure that they seek from these sins.
As for marriages lacking sexual relations, to your point, they can still be joyful (look at Saint John of Kronstadt and his lady, Elizabeth, for example. Their sort of marriage was in and of itself a rare form of Orthodox ascetic arrangement known as a “white marriage”, albeit the exclusive purpose of this lack of sex was to further dedicate themselves to God rather than for any secular reason), but this is, of course, not the case for everyone. Saint Paul writes that it is “better to marry than to burn with passion.” If that passion remains burning throughout a marriage, however, then one purpose of that marriage has been lost for that couple, and so they will be faced with distraction and irritation when they could be bonding in the flesh to have children and to further love one another. To toss away that capability to make love with a spouse when one clearly longs for it would be as if someone had prepared a bowl of stew for himself because he was hungry, only to pour it out into his sink senselessly. So, certainly, some can marry without facing that flame of fleshly desire, but only some.
