Can a person be a evangelical and also be gay?

Can a christian go to war on innocent others and still be a christian?

Good question.
Here are some of the criteria for a just war:
http://www.holycrossjustice.org/JustWarCriteria.htm

In my mind every possiblity of avoidance would have to be exhausted before proceeding.

Having said that, the question that comes to my mind is "Would Jesus ever advocate War?"
My answer is an unequivocal "NO". Jesus said, "Put your sword in its place, for all who take the sword will perish by the sword."
I think Jesus recognized that peaceful protest was the only manner making change in the system, and the world bears witness to this with examples such as Mohandas Gandi, Martin Luther King, Rosa Parks, to name a few.