Coming out of Bob Evans just a bit ago, a older gentleman came in with a button to the effect of "a person of faith in favor of LGBT rights." Not that such folks don't deserve to be treated as fellow citizens in the workforce and in other areas, but applying that take to marriage is a bit of a stretch.
I've got a soft spot for people getting teased, since I got more than my share as a kid. That gives me a soft spot for minorities of various types, which includes gay-bashing. That being said, same-sex marriage seems to be a bad idea, both from a scriptural standpoint and from a public health standpoint in such that some unhealthy sexuality is being normalized.
However, that goes right past the fans of same-sex marriage, since your secular types will lead with equality as their battle cry. If you ignore tradition both secular and religious, there isn't a compelling reason not to let two folks who love each other to get married; there is also not a good case not to let more than two folks who love each other get married.
That applies to folks who ignore religious thought all-together and to folks who ignore everything but the Gospels, giving use the "Jesus never said anything about..." gambit. For those folks, the counter-argument seems dated and hateful.
Dated, maybe; "timeless" would be a better description, but your mileage may vary.
Hateful, not so much. At least not from my vantage point. Disagreeing with someone's deeper urges can seem hateful; one can hear the sitcom teenage daughter slam the bedroom door and yelling "I HATE you!" to her folks when they turned down her request to do something not in her best long-term interest.
Not much I can do with that short of letting the Holy Spirit do an overhaul on the other person's take on things (or have Him do an overhaul on mine, I hear the left wing of the Peanut Gallery say; good luck on that one). That makes this an unfun topic.