I'm a student in 'the ends justify the means' school of thought and I think Vlad's actions were justifiable. You have to keep in mind that his brutality was born out of the experiences of his youth and the need for desperate and effective measures in the face of considerable odds. Even the pro-Vlad propagandists like to overlook the fact that when Vlad was younger he and his brother were sent by their father to stay with Sultan Mehmet as hostages in order to secure loyalty. Unfortunately, unlike most royal hostages neither Vlad or his brother were well treated. In fact Vlad was abused and thrown in a Turkish dungeon while his brother who was blessed with good looks was... the target of the sultan's repeated amorous advances (read as... raped). This kind of experience will make anyone more likely to rely on brutal tactics to achieve an end.

Vlad's use of guerilla warfare and the mass impalement of Turkish prisoners worked and was instrumental in forcing the Sultan to cease his invasion and keep to his side of the border.