Well, it seems to me that the first and foremost act of love one is obligated to perform for a gang of murderous thieves is to stop them from committing evil. This works in most systems of ethics, whether you are concerned about their karma, their immortal souls, or their dignity and possibility for fulfillment as living humans.
Once they are stopped, I can consider the possibility of redemption. But they have to earn it.
So, is love earned? Or is it given?
Romantic love is earned, obviously. And just as obviously, that is not the kind of love we are thinking about when we say, "Love your enemies." And is love about power, or powerlessness? In the case of love for another human being, either romantic love or filial love: is the purpose to exert power over the beloved? Or to be vulnerable before and with the beloved? And isn't such vulnerability predicated on the risk of being powerless, or abandoning all claims to power in the presence of something made better as you are made weaker?
Is love about gaining control? Is love about superior power, forces, abilities, strengths? Do we lock up criminals because we love them? Do we execute murderers because the State loves them so much? Of course not.
Are we, even, our brother's keeper? Are we obligated to stop someone from doing something we know is wrong? That is, in fact, the argument of fundamentalists who want to convert you to their beliefs. Some sincerely believe that you will be lost if they don't "save" you, and some even believe they will be lost if they don't "save" you. But it comes to the same thing: they must stop you from committing evil, even if "evil" as they define it, is simply the wrong belief, or even non-belief.
And finally: is loving your enemies about redeeming your enemies? Do you have that much authority? Do you have that much responsibility? Do you have, even, that power, the power of redemption or damnation?