So, it is OK (to whomever) to censor when we can make a buck?
Yes, because Google is a corporation whose responsibility is to its shareholders, not to the people of China.
If search engines censor to make a buck, where is their line drawn (to make a buck)?
They draw the line when they run a cost-benefit analysis and find that making that buck harms their reputation by more than a buck's worth.
"Don't be evil" is a very good motto because it makes people believe that the corporation has ethics and responsibility, rather than being a mindless money-making machine. The people running Google have just decided that they can best make money by endearing themselves to people.