Are Tourist Ripoffs Okay?

Say you are a tourist in a third world country.  You go out to a local restaurant for dinner and have an amazing meal for $5.  You are happy and satisfied.  Then you find out the local people have a separate menu with separate pricing and they'd pay 50 cents for the exact same dinner.  Do you feel ripped off or that it's a normal part of being a tourist?

I've read a few things lately saying you shouldn't feel ripped off because this is how the world works.  You aren't a local so you get charged the higher prices because you can afford it.  You come from a country with a higher standard of living so you should be paying something back.

That's making a huge assumption that the person I want to help out in the local community is the owner of the restaurant and not say an NGO that helps street kids develop skills.  

I don't think one or two experiences are going to make that much difference and, like most sane people, I'd never get into an argument with someone over a few bucks for a dinner that still costs a lot less than I'd pay at home anyway but, when you travel and you are constantly seen purely as a source of money, it does get tired very fast.

It's been quite a number of years since I've had that issue because I've not travelled to countries where the standard of living is much different from what you get at home but I remember getting very irritated when I went to Vietnam about 10 years ago, to the point where I didn't want to leave my room.  I met some pretty awesome people but the majority seemed to only be out to get money from me for an overpriced gaudy souvenir or be calculating the maximum profit.

And it works in the other direction too.  I've had people ask me why I'd want to travel to Japan when it's so much cheaper to go to Thailand or other SE Asian countries.  They don't think about why those countries are so much cheaper, that you are profiting from low wages and a low standard of living.

These the whole argument of how tourism can wreck the local economies and whether it is a good thing but that's more than I want to get into here.  

I guess all you can do is try to minimise the bad experiences, try to get off the tourist travel and to keep your wits about you.

I'd love to know how other people cope with these kinds of issues when they travel.  Tell me...