More like the other way around. You'd be willfully giving them access to your character (and account), which makes it far easier to steal not only your gold, but also your account info. That rule is largely in place to protect YOU.

@ Onetrueping - What if I wanted to wave the protection? I should have a right (in a sense) to wave any legal obligation towards Blizzard if my account information was stolen. If I choose to gamble with my identity, it should be my choice. Blizzard does not offer this, but I would hope they would in the future.
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I agree 100% with you, Wellandus. I look at the power leveling services this way: I pay $10 for a *brand* wrench. I get a leaky sink. Now, if I am fully knowledgeable to understand how to fix that sink, I could do it. However, if I am lazy, taking care of a family, and/or working 10 hours a day/5 days a week, I could pay someone to come over, use my wrench and fix the problem for me.

I should be able, in WoW, to pay someone to use my account to power level one of my characters. Now, I do NOT use these services, but I can understand full well why someone would use them. And besides the 'it's blizzard's game and what they say goes' argument, I still haven't come across anything to give reason to not be able to power level.

-Aticus, http://www.paladintales.blogspot.com

Wouldn't it be more like giving a stranger your house keys and telling them to come round when you're not there to fix the leak.

If you were stolen from, you can bet your insurer would be reluctant to pay out. In this instance you can look at Blizzard as being the insurer, as you'd expect them to correct things. They're explicitly warning you not to give your house keys to strangers so the situation won't arise.

@Aticus:
In the TOS it says you cannot share your account with anyone. By allowing a powerleveling service access to your account you violate the TOS. You are the licensed user, your license does not allow you to sublet the content or service to another person.
Cut & dry.