>but since Steem Power can't be powered down immediately removes the fraud issue. 

No, it doesn't , unless there is also a way to "charge back" the purchased steem power once the credit card gets charged back.

Yes, a fraudster won't be able to immediately monetize by buying steem power then charging back and selling his illicitly purchased steem power for cash, he would still be able to get full value and use from it (as well as selling powered up accounts)...

I kind of looked into it, and Its doable if you had the right sort of merchant account and a pretty robust anti-fraud system....   but it would be risky as all get out because if someone figured out a way to game you, they could take you for quite a bit fairly quickly.