I'll add another hypothesis. There are plenty of simple, harmless ways to induce pain of almost unlimited intensity, while doing the same with pleasure tends to involve nasty side-effects. Due to neuroplasticity, we can train ourselves to get our pleasure/pain wires crossed, thereby making intense pleasure "cheaper."
This would explain why children often at first dislike spicy food, horror films, roller coasters, etc.
I'm not sure how much this applies to "being Bruce."
Due to neuroplasticity, we can train ourselves to get our pleasure/pain wires crossed
I find this claim highly suspicious, because the little bit I know about neurobiology tells me that pain and pleasure are controlled by neurotransmitter chemicals, not by synapse connections (wiring), and so it should not be possible to cross them except by genetic defect.
Followup to Stuck in the middle with Bruce:
Bruce is a description of masochistic personality disorder. Bruce's dysfunctional behavior may or may not be related to sexual masochism [safe for work], which is demonized by most people in America. Yet there are ordinary, socially-accepted behaviors that seem partly masochistic to me:
Question 1: Can you list more?
Question 2: Doubtless some of the behaviors I listed have completely different explanations, some of which might not involve masochism at all. Which do you think involve enjoying pain? Can you cluster them by causal mechanism?
Question 3: When we find ourselves acting masochistically, should we try to "correct" it? Or is it part of a healthy human's nature? If so, what's the evolutionary-psych explanation? (I was surprised not to find any evo-psych explanations for masochism on the web; or even any general theory of masochism that tried to unite two different behaviors. All I found were the ideas that sexual masochism is caused by bad childhood models of love, and that masochistic personality is caused by other, unspecified bad experiences. No suggestion that masochism is part of our normal pleasure mechanism.)
Some hypotheses:
My guess is that, if it's a side-effect (e.g., 3) or a non-causal association (4), it's okay to eliminate masochism. Otherwise, that could be risky.
These all lead up to Question 4, which is a fun-theory question: Would purging ourselves of masochism make life less fun?
ADDED: Question 5: Can we train ourselves not to be Bruce without damaging our enjoyment of these other things?