Megatron tends to become so obsessed with the object of his desires that he can ignore "secondary" matters, glaring flaws in his plans. Otherwise, he likely wouldn't have chased after the AllSpark alone, and spent centuries entombed in the Arctic. Trying to talk Megatron out of blindly going for his goals is useless. He will risk his world, his troops, and even his own spark to achieve his goals; these things do not matter to Megatron. Like his master, Megatron hates humans.