The common pro-gay-marriage argument is "Banning homosexuality or limiting the rights of homosexuals is basically discriminating groups of people for who they are." (to quote Redundant) Is this a logical argument?
The main assertion here is that it is wrong to discriminate between people based on who they are.
Of course, we can all agree that discrimination is fine, for example we put criminals in jail, can we apply the same argument to jailed criminals? Well, Redundant specifically says "Homosexuals do not harm others by being who they are" - that is, they aren't an intrinsic threat. Jailed criminals are assumably a threat in some way, maybe they didn't pay parking fines, maybe they abused their children, maybe they were jailed for insider trading. These are things that we have recognise as wrong. But why do criminals do these criminal things?
Modern theory indicates that biology and social factors both play a role to some degree.
http://www.nytimes.com/2011/06/20/ar...anted=all&_r=0
http://www.aic.gov.au/media_library/...f/tandi263.pdf
I won't bore you with spammed links, but there is a general consensus that you can have a genetic disposition to being a criminal, but that social factors (whether economic, geographic, your family, your community, etc) are important too.
So ignoring the "do not harm others" clause, we say that some people are criminals in the same way that some people are homosexuals? Is it right to limit their rights?
Currently sexuality is seen as a product of biological, hormonal and social factors. So are mental illness or genetic disorders? Are we wrong to give them drugs, treatment, maybe even isolation and special treatment?
If we are to accept the argument that "Banning homosexuality or limiting the rights of homosexuals is basically discriminating groups of people for who they are." should we accept it for all other similar situations?
Why is it OK to discriminate if someone has caused harm to others (or their property, more commonly), but not if they have not? Do homosexuals really not cause harm to others? Considering the constant unrest that has been caused in many countries as a result of their collective actions (aka not caused intrinsicly by their existence, but because of their political actions or otherwise), is it a fair assessment to say they do not cause harm?