It's far from dumb. It is an issue of where does the line get drawn. Obviously there are groups like NAMBLA that want legal relationships with young boys. What determines the legal age of consent? If the marriage definition is changed, then other groups are going to push for their acceptance as well.
Okay, not so quick in, quick out. Damn discussions of homosexuality! Damn you discussions to Christian hell!
Regarding your post, it's hard for me to take people that have the concerns you express in this post seriously. I mean, it's like common sense absolutely vacates you when it comes to this issue.
18. 18? Isn't that the age we legally establish as an adult in the US for all ostensible purposes?
So, let me break this down for you in simple, comprehensible guidelines for navigating through this issue that, for some reason, individuals like you have to make far more complex than what it really is:
1. 18 is the legal adult age in the US.
2. At (or after) age 18, any two consenting adults should be able to get married.
3. Anyone under 18 is, by legal definition (already defined by our courts), not an adult, and, therefore, could not consent rightfully to a marriage, although we have admittedly let 15 and 16 year olds get married in our nation's prestigious marriage past.
4. Point 3 means that a person wanting to marry a kid (say a NAMBLA activist) will not happen.
5. Anyone and anything not a human being cannot, by legal definition, be a consenting, sentient human adult.
6. Point 5 means that a person cannot marry anything other than a legally-defined human adult.
This is all already been defined for you. What's so difficult to understand?
Gay men just icky or something?
And, regarding polygamy, while I find that a valid concern, it subverts any religious arguments against gay marriage (which are pretty much the only arguments against gay marriage that exist because thinking gay marriage is bad requires suspension of rational thought just like religion). Therefore, your objections are pointless and mute.
Okay, now I'm done.