Why is it that so many things that feel so good are so bad?
Take for instance Coconut Cake. A well made version- moist, sweet but not too sweet, light and dense all at once- literally feels like pure happiness melting in your mouth. The high from this rare delicacy transcends any food related serotonin boost. But then you must come to terms with the fact that Coconut Cake is the devil. It is really really bad for you. Enjoyed more than once a year could be dangerous and detrimental to your jean shopping.
But there are more substantial life unbalances of good vs. evil. You know the story- the girl loves the bad boy* and the bad boy gives the girl tiny morsels of love but in the end the bad boy is quite bad and she pays for it. Why does this happen? We know the second we meet a bad boy that some chemical reaction we have no control over has possessed and overtaken our body functions (*bad boy = person who knowingly shows signs of 100% chance of hurting you in some way or form). We're like high zombies. But it feels so good! And then, when he scoops your heart out with a spoon, the low is much lower than the high ever was. But it's a classic story.
And then of course drugs, alcohol, sex (this is only bad if you're stupid)...the list goes on and on. I'm sure you can imagine many. Life's greatest pleasures acting as a cocoon over a nasty bout of badness.