Is banning “gay marriage” discrimination? No. Under the legal system prior to the legalization of such unions, anyone was free to marry someone of the opposite gender, no matter your gender, race, religion, economic status, or sexual orientation. You are free to marry someone of the opposite gender, and the law is applied equally to all people, so banning “gay marriage” is not discrimination.
As far as homosexuals being allowed to do what they desire, why not let anyone from a cookie thief to a child molester do what they want, homosexuals included? We ban certain things because in a society, culture matters — if we live in a culture of sexual perversion, we will get the consequences of that culture.
If the gays want to win their argument, they are going to have to re-tool their propaganda machine — the current line is too obvious a lie.