“Christians are told to love their enemies, so that means they want to hold their hands around a campfire singing Kumbaya, right? How pathetic. I want to torture and annihilate my enemies by any means necessary. Clearly, I am brave and willing to do what is hard.”
Our friend there who I just made up has entirely misunderstood what the question at hand means, and it’s likely not his fault, because nobody is likely to have told him. He has grown up in a toothless and progressive nation with a vaguely Christian veneer, and equates those things with a high level of confidence.
Christian rulers crushed their enemies in Europe, Byzantium, Iberia, Latin America, Russia, Africa, and more. At the same time, they loved them. How?
The more that I've learned about philosophy and theology, the more I've realised how absolutely terrible the modern English language is at communicating it; so much so that it makes me want to put on a tinfoil hat and say that this has been done deliberately, specifically to obscure these incredibly important points. To illustrate, there are 8 different words in Greek for “love” and we’re left with just the one, which has entirely different meanings dependent on its context.
So the first point is that love, used here, does not mean eros, philautia, storge, mania, or pragma. It means agape, the selfless kind of love for all others - translated to Latin as caritas, then to English as charity. St. Thomas Aquinas defines this love as:
The choice to will the good of the other.
So, can you will the good of your enemies, even as you fight them to the death? Absolutely. And trust me when I say that this is far harder, and requires far more courage, than willing the worst for them. Hating is easy, loving requires true strength. And don’t forget that Christ, in telling us to love our enemies, is explicitly saying that we have enemies. He is not telling us to make peace with evil, He expects us to fight it, and to win.
Now what is the “best” for your enemies? It is the same as what is best for all humans: perfect communion with God in the beatific vision, more commonly known as going to Heaven. This is man’s telos, or ultimate end - the summary purpose for his entire existence. Everything we do should be for this alone, and everything we do which does not advance this, and pulls us away from God, is called sin.
Still, this is all well and good, but why should I will this for my enemies, when they are evil and I am not?
Because, without the blood shed by Christ on the cross, nobody can get there. You don’t go to Heaven for being good and you don’t go to Hell for being bad; where you go is entirely dependent on your love and acceptance of God, who loves and accepts you. The nature of fallen man, us being imperfect, means it is impossible to go to Heaven - the place of no imperfection - on our own.
You, I, your enemies, your friends, the most evil and the most good people in all of history, would all be damned if it weren’t for God’s mercy. We imperfect creatures cannot make ourselves perfect as we obviously only have imperfect means at our disposal. The only thing which could do that is the perfect, the Good, and He offers this to us out of love. Love cannot be forced upon a person, it must be accepted, so God’s love truly is there for anyone, all they need to do is accept it. He wills the best for us, as He tells us to do for others. Wouldn’t we owe Him that at the very least?
Pagans (including atheists) will still be unhappy about this, as they don’t want to worship God. They want to worship the self, and believe they are their own telos. They believe that what you do in life is all that matters; you have to be vaguely good and strong and that’s enough. Sadly, that's the bare minimum, and the easiest part.
Here’s a secret: everyone wants to worship the self. We all want to care for ourselves above all else and to only help others if it’s convenient or benefits us in some way. Selfishness is the cornerstone of our imperfection - but the truly good, strong, and brave man, doesn't just do what he wants; he does what he should. And man should strive for God above all else, the same God who can’t not exist for He is existence itself.
There is no denying His reality and our total dependence on Him, and there is no escaping the duties we have because of it. You can start by making evil your enemy and loving the people who hate you for it, whilst utterly defeating them.