The criminal, civil, and ceremonial laws of the Torah, in this case, capital punishment for homosexual acts, were specifically for the ancient nation of Israel. But the moral foundation of that law is true for all humans. Similarly, while the laws that would/should have made capital punishment rare in the ancient nation of Israel - having to do with burden of proof, to use the modern term - are also specific to Israel, their foundational wisdom (what we call "proof beyond a reasonable doubt") is true, generally.
I believe that the criminal laws, for the most part, are in line with the moral laws. The punishments for the laws, however, are not bound to the moral laws out side the Hebrew society. Homosexuality was wrong under the Torah and is wrong when viewed through the lens of Christianity. Hebrew society could punish the violation with death, Christians however are taught to seek to forgive homosexuals and encourage them to repent. If they choice not to repent then punishment, if any, is left in the hands of God.
The whole concept of love you enemy is, in my opinion, based around the idea of letting God deal with punishment for moral sins that are not addressed by social laws. This does not mean that a society can't choose to punish crimes that it feels violate its social order.
The whole area of what Christians can and can't do can be confusing. I believe that God would want Christians to encourage society not to implement the death penalty on homosexuals for the fact that they are homosexuals like we are to encourage society to have laws that make abortions illegal.
Most of this is just my opinion derived from reading scripture and using scripture as something that provides examples of God's desires. I try not to introduce my own feelings in to things because I am a fallible human but sometimes it is hard to be completely unbiased.