Is being handicapped normal? Does that make wheelchair ramps a "special right" for folks in wheelchairs?
Sicknesses and injury are common in the natural world, but that does not make them normal states of health. Since when is paraplegia, for example, a normal state of human health? And allowing a handicapped person access to a public place is simply ensuring them the same right to be there as anyone else.
...the same rights as straight people - that is, marrying the person that they love.
Marriage is an ancient and sacred (in countless religions and cultures) union between a man and a woman for purposes of procreation and child-rearing. "Love" isn't even considered in many cultures where marriages are arranged long before the betrothed individuals even understand a concept of romantic love or sexual relations. If homosexual couples want to engage in sex or romance or living together, fine. But change the fundamental concept of marriage so they can pretend to live in a normal marital relationship? They can't procreate! Better to legalize it as a "gay union" than as marriage. But even then, why discriminate against all other types of people who happen to live together? Provide all of them the same privileges that a man and woman trying to raise a family have. Why are gays so special?
By the way, if you are an evolutionist, how do think homosexuality, if it is a normal condition, evolved as an adaptation that is beneficial to the propagation or survival of an individual's genetic traits? It may be "common" in the natural world, but I still maintain that it is not a condition that is normal.