From my experience, the happiest marriages are of people who don't just "go" to church, but actually try to "live" their church's teachings in all areas of their lives. Churches usually promote selflessness, sacrifice, honesty, gentleness, and sincere love. So it's a recipe for happiness inside or out of marriage, but especially inside marriage.
And some churches have particularly well-developed theologies of marriage and family. See, for example, Pope St. John Paul II's apostolic exhortation Familias Consortio and its many church-teaching references (and, in turn, their references and so on).
For the record, I did that. And from the inside it appeared to work. For years I thought I was happy and had a fantastic marriage. But it still didn't prevent us from ultimately coming to the conclusion that staying married was not the best thing for either of us. Now I'm agnostic and MUCH happier.
YMMV. Other churches promote killing everyone that don't believe in the same god, or believe in the same god but have a method to pray, or has other social habits.
I think that it's not a problem of a specific religion. Most religion has peaceful periods but 300 years later the "same" religion has a violent period and 300 year later the "same" religion is peaceful again, ...
And sometimes, some members of the same church are peaceful and some are violent. It's more complicated.
Churches/religions can condone violence to others while still promoting healthy marriage, so your point doesn't necessarily mean anything about the topic at hand.
(Obviously, your point is important in a larger context. :)
