One could construct a case for feeling sympathy for Macbeth because it is clear he is not in control of his actions. Macbeth is out of control and is incapable of knowing the difference between right and wrong. In seeing he and his actions, it becomes clear that he is not in control and that other forces such as unchecked ambition and desire are in control of him. Seeing anyone relegated to such a condition might stir some level of sympathy.
That being said, it is really difficult to generate sympathy for anyone who orders the slaughter of wife and child. Macbeth is killing innocent people, civilians who have little to do with his own desire. Lady Macduff's murder and the murder of her son is beyond comprehension. Even the most liberal of viewers would find it difficult to have sympathy for the commissioned killing of a mother and child. Macbeth's barbarism and savagery are on full display in Act IV. With this, it is difficult to find sympathy for him.