Is it possible to be a gay Christian?

[BeeDeePee]

Matthew 5:17
"Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfil them."

And he fulfilled it. He fulfilled what was written - the Oikonomia of Salvation. That doesn't mean that he was telling the people they should obey the letter of the Law, because he himself did violate some Old Testament rules (healing on Sabbath etc). He also clearly made a distinction between the essence of the Law and its external form, giving priority to later. That's why he has criticised Pharisees for hypocrisy, because they were worried and committed to fulfill some external forms, ceremonies and impersonal moral rules.
One of the basic rules when you interpret the ancient text is to take it as a whole and then interpret it.

But how can a theist argue that a verse saying clearly 'you should kill these people' can be interpreted with a different meaning? Sometimes it just looks like they are trying to hard to hide hideous literal meanings in the holy scriptures

Better ask some Christians who do that. I disagree with that kind of interpretation because I think it's meaningless. It's nothing else than incorporating your meaning into the text.