Personally, I find homosexuality to be perfectly acceptable. I am not gay myself. I do have one gay friend, but that friend isn't that close to me.
I base my opinion on the idea that they aren't harming anything by being gay. The only possible consequence is the spread of STD's (because of the type of sex that is practiced), but if they are educated enough they know to use protection.
For the religious argument. We (The United States atleast) AREN'T a theocracy, christian democracy, etc. (although many in this country would like to change that I'm sure). We are simply a democracy. In that the government should neither sponsor nor prohibit any religion. See the first amendment.
On the topic of marriage. Although we need to respect homosexual rights, marriage is defined as a bond between a man and a women. We should never change that, however what what should be administered is the opportunity for a legal bond between homosexual couples (allready exists several places I'm pretty sure). Essentially this would be like the "separate but equal" doctrine, whereas homosexuals could enjoy ALL the same legal benefits as heterosexual couples but it would simply be givin a different title.
On the topic of adoption. I'm kinda iffy on this one. At this moment in time homosexuals probably shouldn't be allowed to adopt, simply because of all the anti-gays/homophobes out there. The child in many cases would be riduculed beyond belief by their peers (as much as I hate to say this). Eventually, as a whole, our society will be accepting of homosexuality. Until then though, homosexual adoption would be too much of a culture shock to the religious right in this country.
On the topic of reproduction. Come on, who cares if they can't have kids. The world is overpopulated enough already. The bible may say to "be fruitful and multiply" It mean't well, but keep in mind it was written in a time when you'd be lucky to get 2 of your 10 kids to survive through infancy. Now that infant/childhood deaths are relatively out of the picture, you don't need to have 5+ kids to keep the human population going. Better yet, couples not having any kids is GOOD for our world. It compensates for the many who treat the above as a written law.
Basically I feel the same way about this issue as I feel about most religious-type issues. You may believe something, but that doesn't mean everyone believes it. Why should we discriminate against something or someone that isn't harming anyone or anything? That's one question that always seems to go unanswered.