I suppose I could rationalize it by saying that each of the Deadly Sins listed takes a normal and healthy appetite and distorts it into something grossly unhealthy.
For instance, Lust would ordinarily be Attraction, that lovely zing you get on seeing the person you like. Taken to extremes, Lust becomes a sexual obsession and addiction, and the pleasure it creates is destructive, therefore not “true pleasure”.
Gluttony distorts ordinary Appetite until the person is compelled to eat to the exclusion of everything else, and that compulsion destroys the true pleasure taken in good food eaten for good reasons to support good health.
I can’t pin a term down to describe Greed in its harmless phase, but it exists. The things we acquire that satisfy a desire for material wealth mean that we have a viable economy, meaningful work, and a life of relative comfort. Again, when it’s distorted, all these things are thrown out of balance, and the things acquired become the end, not the means.
Sloth is a distortion of the rest necessary to balance out life. While the Torah and the Bible mandate the Sabbath, a day of true rest, those who take that rest out of proportion fail to do the work necessary to keep body and mind whole as well as take part in their community. Whatever pleasure is gained by rest is negated by the loss of those qualities won by healthy effort.
Wrath is the outgrowth of anger, and anger is a healthy, appropriate emotion to many circumstances and spurs us to change those things we find unjust and unfair. Wrath, however, consumes a person and destroys their ability to mete justice with deliberation, objectivity, and fairness. Whatever pleasure might be gained by, oh, cutting a rapist to pieces, penis first, is poisoned by the fact that the wrathful person is now also a monster.
Envy, or the baby version of it - again, I can’t think of an appropriate word - spurs us to improve ourselves. Envy is admiration taken too far and turned destructive. Instead of matching the person we envy, we try to destroy them, and most of us, I believe, find less pleasure in things we steal that in those we earn.
Pride/vanity is a shell covering insecurity, and those who indulge in pride may feel like they present a seamless, perfect facade to the world, their self-knowledge makes it impossible for them to relax and enjoy their talents and attributes. Instead, they must always be on guard, defensive, and querelous to make sure no one gives them less than their due, because then others might question what they really are due.
So, I think C. S. Lewis is on to something. But that’s just me.