This is a two-part question that deals with the bad character on the one hand and with the table drama on the other hand. For the context, I'm currently DMing D & D 5e Curse from Strahd, with 5 players. Some of you may think that this is too much to agree with, but our group has been established as a social element for friends so that we do not want to exclude anyone. The friendly is also why I tried not to be overwhelmed with authority.
Problem 1: I have a player who treats his characters as available
I have a player in my group that I will call Carl. Carl has a constant problem of building one-pony-pony characters, being bored with them when they are not as good as he thought, and then stopping them alive to build another can. I disagree with this behavior because a) a constant death of the character in a story-driven and knowledge-intensive campaign like Strahd is detrimental and b) he implicates the group in his terrible decisions and also endangers the characters of other players. I understand that the death of a character is part of a campaign, but I also believe that campaigns (especially a published one like Strahd) are based on the general assumption that characters try to survive because he is the only one who does. To prevent the death of a player, I have introduced a rule that requires the second character to be built from the point purchase statistics (all values were initially rolled above average) and the third character must use the default array. This rule came into effect when Carl's character died for the first time (he tried to fight against Vladimir Horngaard alone) and he built his next character from the Point Buy.
Problem 2: The player has decided to be a huge baby (but he's in tough times, so I try to be nice)
In this last session (Amber Temple), Carl's character had many curse errors and his direction changed to evil. At the very end of the session, he announced that he would attack the party shortly before a long break. He also played the card "My Guy". Since his death is almost certain next time, I told him to create a new character with the standard array. The next morning, I wake up with a text stating that he lists the statistics for his new characters. If I do not allow him, he takes the Strahd book and the grid card (which he has previously donated for us) and quits. I managed to talk to him about it and he said that he feels I've wrongfully punished him, that he does not think it's a problem for everyone else, that his character is not that good like the other melee fighters (He is an Eldritch Knight with a Barbarian and a Paladin) and he felt that new characters are being treated badly by the existing characters and he is having no fun. The last thing he said was that he might just stop but leave the materials so we can keep playing.
The basic questions are: How do I deal with a player who does not care if his character dies and the group moves into risky situations, and how do I feel like he's playing again? Honestly, if this was not a group of friends, I would have kicked him for his behavior and bought new materials, but I do not want to do that to him. If someone has dealt with a situation that is comparable to one of these problems, I would like to hear about it.