I don't believe I suggested gay marriage would kill anyone. Nor did I suggest it would harm the participants. Of course neither do bestiality or necrophilia. However, neither are supported by tradition western european culture either. I can say marriage has an important role as an institution that supports the procreation and rearing good citizens for that culture. It's much the same with all successful traditional cultures.
I could argue that gay marriage has nothing to do with either procreation or raising citizens. Keep in mind I firmly believe children represent a black hole of need and one of those many needs are two parent of both genders and whenever possible biological. I am a conservative after all.
In regards to gay marriage in the here and now I see this as a political issue. One in which the democratic party wishes to reward a valued demographic for it's support and monies over the years. I see abortion as a result of the same kind of identity politics that also benefited the democratic party decades ago. Do you want to argue abortion hasn't harmed or killed anyone?
Ok. You do realize that I don't harbor any animosity against you or yours. I disagree with your ideas on gay marriage. I reject your vision for this country but that is all.
Beastiality nor necrophilia have provide any benefits for the people involved nor society as a whole. Plus, beastiality and necrophilia are both sexual acts, not sexualities, and are both illegal acts.
Homosexuality is about the attraction of a person to a member of the same sex. It does not involve dead people (who cannot consent to sex) or animals (which also cannot consent to sex). Nor does it have to involve sex at all. It is quite possible for a person to form a loving and even intimate relationship with another of the same sex without having sex, just like it is possible for a person to form a loving and intimate relationship with a person of the opposite sex without having sex.
Marriage is not just about procreation and raising kids. If it were, then many opposite sex marriages would not be allowed, including those when one or both of the partners is infertile or when the woman of the couple has gone through menopause. Also, the government would not be recognizing marriages between cousins from states where those cousins cannot get married unless they cannot procreate. And, to top all this off, the government recognizes the state's view on what the state considers the "gender" of the person within a marriage. So, if a person has undergone gender reassignment surgery and their state recognizes them as the new gender, then they can marry someone of the same genetic sex as them.
Plus, gay people can have children. There could be children from other marriages/relationships. There is surrogacy, and there is adoption. Your ideal parenting situation is not always available for most children, even those raised by their biological mother and father. Any loving parent is better than none, and two are better than one, no matter what their sexes or sexualities.
Marriage serves many purposes, but the one that applies to every couple, is that it makes a person a member of another person's legal family, eventhough the two are not blood related.
There are also other benefits to society that come from marriages, including someone to make legal and/or medical decisions for a person in the event of incapacitation or death. Someone to be legally responsible for the burial costs/decisions of a deceased person. Someone to be legally responsible for the debts of a deceased person. Stable households in which the couple is married are all better for the community, no matter the sexualities of the couple.
The only negative you have is a change in tradition. Which many do not see as a negative at all.