Madara has a second chance at life. But, he still decides to fight the 5 Kage and take the risk of getting sealed. Damm man. The whole shinobi world didn't screw you over, only the Uchiha clan did. So, go find and kill the last Uchiha, Sasuke, then get on with your life. Yeah, he would marked as a criminal and hunted down, but he can bitch slap the bounty hunter and keep moving. Who agrees?xd
1.) Madara grew up fighting others, he's learned not to trust anyone.
2.) Uchiha clan did screw him over, but he believes Hashirama and Konoha also screwed him over.
3.) It seems Nagato was supposed to revive Madara sooner, meaning, someone betrayed him. He might think Tobi did it and needs to punish Tobi.
4.) He believes himself a god and Kabuto summoned him and used him as a pawn. I'm sure he doesn't like that and intends to kill Kabuto too.
5.) Tsunade is a Senju and he doesn't like Senjus. He also doesn't seem to like Onoki. He can't just say 3 Kages leave, I'll just kill these 2. The other 3 will stay and fight so no point chatting, just focus on slaughtering them.
6.) He still wants to fulfill his plan and now his enemy know of it. He's capable of killing the 5 Kages and they are some of the most powerful, so why not get rid of them for future sake?
He's just full of vengeance. In my opinion, this is foreshadowing of what will become of Sasuke. A being that believes the entire world is against him and the only solution is to destroy them all or enslave them all.