Matt. 5:44 But I tell you: Love your enemies and pray for those who persecute you...
Certain Skeptics think that Jesus missed the mark in living up to this admonition. Here are some examples, and the answer:
Matt. 23:17, 27 You blind fools! Which is greater: the gold, or the temple that makes the gold sacred?..."Woe to you, teachers of the law and Pharisees, you hypocrites! You are like whitewashed tombs, which look beautiful on the outside but on the inside are full of dead men's bones and everything unclean.
Matt. 12:34 You brood of vipers, how can you who are evil say anything good? For out of the overflow of the heart the mouth speaks.
John 10:8 All who ever came before me were thieves and robbers, but the sheep did not listen to them.
A key here is understanding the function of polemic in first-century Judaism. It is certainly possible under these constraints to love one's enemies and pray for them, and also attack them polemically, though such complexity of emotion is quite often foreign to us.
Moreover, the term "love" here does not correspond with our modern psychological category; it is "not a matter of sentiment and emotion but concrete action and practical concern." [Hill's commentary on Matthew, 130] It is in fact the term agape. It does not exclude verbally attacking and discrediting one's opponents when they are in the wrong. (See links below.)
Beyond that, Jesus speaks to these men not as his enemies, but as enemies of the truth. There is no indication that he speaks to them as personal enemies, for all of his comments reflect their deception of others. The ancient definition of agape did not exclude polemical practices against ideological opponents who did broad, general harm to others, and so Skeptics are merely illicitly applying modern categories to the situation.
One would hardly suppose that Matthew 5:4 would restrict one from joining an army and fighting in a war against a Hitler or a Stalin. This becomes a case of having agape for the greater number, and generally innocent, at the expense of the lesser who are guilty. Jesus' situation with the Pharisees and others attacked was very much in this category, since their actions imperiled the eternal fate of others.
An extra note on John 10:8 - it has the semblance of being literally true. Horlsey (see generally Bandits, Prophets and Messiahs) notes that those who expressed messianic or kingly ambitions were indeed often thieves and bandits. But even if this were not so, then obviously anyone who was not the true Christ but proclaimed to be would indeed fit the description.