I get the outrage - and it IS fair that consultants get paid. Often you are dealing with a founder who has no resources, so they have to beg, borrow and promise. They aren't trying to screw you, but often the entrepreneur is trying to make the impossible, possible - and finding delayed compensation is a tool to help you achieve the impossible.
Don't be outraged that someone asks you to do labor or for expertise without immediate compensation - just make it clear in your early discussions that you need to be compensated in cash. If you would entertain getting compensated in equity, then don't be surprised if the founder jumps all over that - equity is a currency that they have and value highly - and they can spend it on you and get what they need in order to make that equity worth more, what a fantastic win.
But their goal is not to extort anything from you, but rather to pay you with what is most valuable to them - a part of their dream. Don't look askance at that - dreams are most powerful when shared. But if you don't want to, or can't work for equity, then make it clear and move on. No harm, no foul.
And here is a prospecting tip for consultants/programmers/designers/etc. - startups pay like crap. You aren't going to get market value for your services because they typically lack cash. So, if that is your concern, rev up your sales game and target bigger fish. Startups use low cash compensation and shared opportunity as their currency. Don't be offended - it isn't because they don't want to pay you - most often, they can't.