Laws can allow for immoral things because the people writing the laws feel the benefits of flexible interpretation outweighed the unlikely risks of abuse. For instance, free speech is protected in the United States Bill of Rights. Sure, I can use my protected free speech to tell the whole world that Tom Cruise is having problems in his marriage, or that he's really embarrassed about that new growth he has on his left butt cheek. However, in doing so I'm acting somewhat immorally, taking advantage of someone else. It's a fine line on a slippery slope coated with turtle wax, but it's something to look out for.
I put the majority of my books out as Open Content because I want other publishers to be able to use any rules they like in their own books. I want to foster the gaming industry, so that rather than three people creating redundant rules, they can pick what they think is best and use that.
It is not so much me saying "Everyone use this free" as it is me saying, "Well, US Copyright law is a mudpool of complications and difficulty, so the OGL is a pretty good solution. I just hope people don't sabotage the whole effort of enhancing the art of game creation by using the OGL to hand out all our work to people for free."
Without the OGL, collaborating and using rules created by others would be a pain in the ass, and fraught with risk of getting into legal issues. So yeah, I use the OGL because it's the best thing available. If there was a license that could manage to clearly state the letter of the law to match the spirit of "use this to help produce quality gaming products," I'd use that instead.