In Animal Farm, animals tend to believe every piece of information from the pigs, even though the pigs lied to them. That leads to the point that animals need to think together to come to a correct conclusion. What are the reasons they should learn how to think and make up their mind?

If the animals thought for themselves, then they'd realize that Napoleon doesn't rule in their best interests. He's a power-mad dictator, a control-freak who isn't happy unless he's telling other animals what to do and how to live their lives. More ominously, he wants to tell the other animals how they should think; he even wants to control their thoughts. At Manor Farm, the truth is what Napoleon says it is, forcefully backed up by Squealer, his chief propagandist and, like Napoleon himself, a pathological liar.
If the animals realize that they can think for themselves, then the rule of the pigs will be history. Then at long last everyone will be able to see that there's nothing inevitable about the complete mess the pigs have made of running the farm. That doesn't mean that the humans need to return to run the place; the animals will understand that it's possible for them to remain in charge but without the chronic waste, inefficiency, and brutality of Napoleon's regime. In other words, thinking for themselves will allow the animals to realize the true spirit of Animalism, instead of the grotesque distortion handed down to them from Napoleon.