How have prominent apologists answered those who claim that Jesus does not love his enemies?

Remember that, first and foremost, our condemnation is just because we all have sinned. However, because of His love, Jesus died for us while we were yet sinners. He was under no obligation to save us in the first place.

Our situation might be likened to a man trapped in a fire. With his death impending, a fireman found him, carried him to safety, and saved his life. If the fireman did not save him, the man would die first and foremost because of fire. We are condemned first and foremost because of our sins.

That Jesus died for us is in fact the ultimate display of His love for His enemies---all of us, who hate Him. This is actually the good news (gospel) that Mark 16:15 talks about. If we reject this gospel offer, we will be condemned, because there is no other way for us to be saved.

Maybe a classic parable will help:

Imagine a man broke into your house and murdered your dearest loved one, and then he got caught. Imagine him being in court and he swears he'll never do it again. Imagine that somehow through advanced technology you knew that he was lying. Imagine also that he is demanding he be let free because his act of murder "wasn't that big of a deal."

Finally, imagine the judge, knowing all these facts, saying something to the effect of "You've committed a horrible and intentional crime and are unrepentant of it. The law says you should be executed. However, I am a loving judge--so I will let you go free."

Who, in their right mind, would consider that judge to be a loving judge? We'd consider him to be an evil fool. And yet the very thing you claim Jesus should do is what this judge is doing in my story.

Such is the case for people who don't believe in Jesus:

John 16:8,9 ESV And when he comes, he will convict the world concerning sin and righteousness and judgment: concerning sin, because they do not believe in me;

Romans 3:23 ESV ...for all have sinned and fall short of the glory of God

Matthew 12:36,37 ESV I tell you, on the day of judgment people will give account for every careless word they speak, for by your words you will be justified, and by your words you will be condemned.

You may say "How is not believing in Jesus such a big deal?" It's a big deal because, according to the God's moral laws as revealed by scripture, we're all guilty. We're all totally guilty. And even if we convince ourselves that we won't break the laws anymore, we're wrong, and we still have to account for the sins we've already committed.

But the way out of this is to accept Jesus' free gift of salvation. The only thing a person has to do to accept it is deny their own "goodness" and accept Jesus'. Love and justice meet perfectly in the gospel. Jesus loves us by offering us a free salvation gift and Jesus is Just by offering himself in the place for those who accept it. A person that is unwilling to do that after a lifetime of opportunity is condemned.

You made the classic mistake people make when they question Jesus' love: they make him a one-dimensional person. So when someone says that God is love, then asks, "then why would God ...," they are assuming that God should respond only in love -- to everything.

In the case of sentencing people to hell, Jesus would be acting in the role of judge. Human judges pass on sentences to those who have broken the law, then they go home and love their spouse and children. So there is no contradiction between love and passing on judgment to those who deserve it. That is not hypocrisy; that is not playing a part of which one is not. On the contrary, Jesus will take up the role as Judge of the quick and the dead in the last days, and he will do it with full authority (John 5:28-30).