When I was a kid, we'd have broccoli for dinner, and my mom would boil it to death with no seasonings (my mom is the worst cook), and I hated it. The answer I got when I complained?
"Of course it tastes bad. It's good for you."
It's a pervasive message in our society, one that goes way beyond dinner: virtue is the opposite of pleasure. Sexual morality is the restriction of sexual pleasure; healthy living is uncomfortable; honest work is grueling; polite living is self-suppressing. If it feels good, it must be illegal, immoral, or fattening.
Obviously, this is not 100% wrong; "if it feels good, do it" can get you in all kinds of trouble. Sometimes grownups just gotta do things that aren't fun. But taken too far, broccoli morality sends some very wrong messages:
"Morality is about avoiding excess pleasure."
Giving up pleasure may be a side effect of making good decisions, but it is never the goal. The mere fact that something feels good doesn't make it wrong. This is a big hitch sometimes in sexual morality--"you're having [nonstandard] sex just because it feels good!" Damn skippy I am.
"Your natural desires are evil."
It's not much of a leap from this to "so yeah, you're evil," and that's just horrible and untrue. It's also not much of a basis for self-improvement. Is it really worth putting that much work into an evil and greedy soul? But worst of all, it makes evil the default--doing wrong is just a slip back into your natural state, instead of something you chose.
"You can never be happy."
If your natural desires are for evil, but you have an obligation to be good, then it follows you're going to spend your whole life in a state of frustration, choking down soggy broccoli until you die. Awesome. Like the last one, this makes evil way more tempting than it needs to be. And it's just not true.
"When you grow up, you're going to have to spend most of your time working and go without most of the things you want" is a half-truth.
The whole truth is "When you grow up, you're going to have to spend most of your time working and go without most of the things you want, but you're also going to have fantastic orgasms and nights you stay up til 5 AM just laughing and books you completely lose yourself in and hugs that seem like they make the whole world right. And you should never, ever feel one bit of guilt about loving those good parts."
Also, when you grow up, you'll discover that there's such a thing as bacon-wrapped broccoli.