Basically, Thawne wants to create his own Flashpoint to replace Barry but after Barry stops his timeline, time itself starts to erase him from existence because he's a paradox so he comes to Barry to get help and survive. Everybody in the team, including Barry and Iris, agree to let him die because he's just a petty sadistic sociopath without any hope of redemption and a monster who made Barry's life a living hell and outright and proudly said he would continue to mess with him...everybody except Joe, who starts ranting about how that's not what heroes do and they should save him because for some reason, if they let a deranged sociopath die out of his own actions, they will become monsters.