I don't want to attack it! Half my alt-coin investment is in Bitcoin! However if someone says it may be possible to attack Bitcoin with 3/4% of the hashing power, I'd like to understand why it's wrong.

To me it seemed like, (To keep the numbers simple)...

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- If there were a $1 Billion in new coins made a year then a pool with 30% hash power could expect to earn $300 million in revenue.

- However Bitcoin margins are tight. How tight? I don't know but I doubt they're making more than $15-30 million profit.

- If 3% secret hash power (or 10% of the pool) was not submitting winning hashes, it would take $30 million of revenue from them, making them unprofitable.

- As you're part of their pool though you would still receive a 97% payout,  $27 million. So you may be at a loss too but only a $1 million or two and for that you get to make the main mining pool unprofitable.

- Hashers would leave the main unprofitable pool for the one a bad intentioned person controls, which could then easily accumulate 51% hashing power.
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That sounds like it may be an answer, why this can't work thanks!