The saudis DO "pay for everything", whether it be the people who produce their oil, who manage their other technologies, or who do their fighting for them. They're lazy and would rather pay others than do it themselves.
If we're going to be there, maintaing OUR interests as well as those of the saudis, we might as well be "paid for it" -- and paid highly.
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Actually, I'd rather send a million troops to saudi arabia that are NOT "paid" by the saudis, but who instead depose the shieks, dismantle the kingdom, and destroy Mecca and Medina.
Then AND ONLY THEN would I be able to say that we're getting the desired results over there!