Ya know, Spider, you almost convince me...
DE@ apples and oranges only in terms of both acts being intrinsically different. The underlying principle, however is not. Just because you think something isn't harmful (your argumnet) doesn't mean people should do it (hence my somewhat over the top examples).
Also, I say that if you want to set up a different type of union for infertile couples or people who want no chidren whatsoever, you'll get no argument from me. They can fall under the same style of civil union provisions that can be given homosexuals.
Since hurt is such a loaded concept, perhaps you should define your term before I deal with that issue. Also, your concept of progress seems a little odd. How is the inevitably higher rate of likely divorce amongst gay people going to benefit any one but wedding planners and divorce lawyers? Given that homosexuals have a higher rate of promoscuity than even heterosexuals, this isn't an unreasonable conclusion.
Ultimately, this goes to Skinwalker as well, there is no logical reason to change the traditional meaning of marriage, but arguably the law could be amended to deal with gay unions and their subsequent issues.