At a family's most difficult time I want to make sure at a minimum that they have the very basic of comforts: the ability to grieve their loss privately and the knowledge that their country is grateful for their loved one's sacrifice and service.
I don't know of many evangelicals who want to deny gay couples their legal rights. However most of us don't want to call it marriage because we think that word has religious connotations and we're not ready to see it used in ways that offend us.