Why Can't We Be Friends?

 is a quest in Fallout: New Vegas. It is given by Philip Lem or Samuel Cooke located in Vault 19.

Quick Walkthrough
If you want to destroy the caves, you will need an Explosives skill level of 60 (or 50 to destroy the caves and the vault). The explosives can be placed on the uniquely shaped green microcline rocks. The C4 will react with a nearby pocket of Potassium which will destroy the caves and the vault.

Detailed Walkthrough
The player can choose to complete one of four options. Either to kill all the Fire Geckos for Samuel Cooke to help his gang create bigger explosives and join with the Great Khans, help Philip Lem seal access to the cave surrendering the convicts to NCR OR joining the Great Khans (Speech 60 required), blow up the mines and Vault 19 killing everyone. After talking to Lem in the Overseer's Office, and talking to Cooke in the other Overseer's Office next door, go to the lower living quarters, there are a few Land Mines and Fire Geckos, so talk to your company before using the elevator, tell them to stay where they are so that they wont run into the mines, because they will attack the geckos (extremely recommended in hardcore mode, but see "Bugs" below for possible solution). From the living quarters find the common room with the pool tables and a hole in the floor. It will bring you down to the sulfur mines. On this floor are the Fire Geckos you have to kill to complete Cooke's quest option. On this level you will also find a rock formation with green crystals in it, here you can use the C4 to either destroy the mines, or the entirety of Vault 19.

Cooke: Join The Khans
After you have killed all the Fire Geckos go back to Samuel Cooke. He then sends you to the Red Rock Canyon to meet with the the Great Khans; where you have to convince Papa Khan to join forces with the Powder Gangers in the vault. After you have convinced Papa Khan, return to Samuel Cooke to finish the quest.


 * The doors to Philip Lem's overseers office will be locked, the only way to get in is through the cave, upon entering the room you find no one there and only a puddle of blood with unidentifiable body parts. Going back and talking to Cooke reveals that he had kill Lem.

Lem: Surrender To The NCR/Join the Khans
In the caves find the green crystallized rock. Here you can choose to blow the caves up (Explosives skill of 60 and 3 C4). Return to Lem and let him surrender the gang to NCR to finish the quest. With a Speech of 40 you can convince Philip Lem to join the Great Khans. He requests you act as a liaison, requiring you to visit Red Rock Canyon and talk to Papa Khan to secure their alliance. Return to Lem once again to finish the quest.

Blow up the caves and the vault
Find the green crystallized rock in the caves. Here you can choose to blow the caves up and the vault (Explosives skill of 50 and 5 C4). WARNING: This will fail the quest, and you will not earn any XP. In addition, you will be transported to outside the vault, where the Quest Failed message pops up.

Journal entries
For Philip Lem:

For Samuel Cooke:

Bugs

 * If following the Lem quest line, the map marker will tell you to go to the "Sulfur Caves" entrance (now blown up and billowing smoke) to find and talk to Lem about joining the Great Khans after talking to Papa Khan. Lem is actually located in the Overseer's Office, and if you've opened the stairs leading to the sulfur caves he can sometimes be found stuck there.
 * If you enter the Overseer's Office from the elevator entrance (Hard Lock) in Sulfur Cave and open the Overseer's Office with the Average Terminal, or just go through this route at any time, you may have some issues with your companions as mentioned above in less detail. When you ascend the stairs into the office your companions become confused and instead of following you up will run out the door back into the caves. If you are at the top of the stairs with a companion and run down they will run back into the vault. It is possible, however to keep your companions with you during this if you manually "push" your companion up and down the stairs. Just crouch and slowly move them and they will glide up, or down the stairs from your push.
 * This seems more like a path finding issue. Your companions will go back the way you came and reappear by your side a few minutes later, the same way they will if you jump from a ledge, (yes, it's an oddity).


 * If the player chooses to destroy the sulfur caves and the vault, but didn't kill Cooke personally, then the ending sequence will still show Cooke still alive and the Powder Gangers terrorizing the Mojave.
 * If the player tries to destroy the sulfur caves only after dealing with all fire geckos and uses the Patriot's Cookbook to boost explosives skill, option for blowing up only caverns does not appear (Bug not present in 360 version; all three options, leave it alone, destroy the cave, destroy the cave and vault, are available when using the Patriot's Cookbook to boost skill above 60).


 * (needs verification) Don't know if this qualifies as bug, but after speaking to Papa Khan to let Phillip Lem join, which he did allow. I returned to Phillip and told him which completed the quest. However, on the quest list on the Pip Boy, it shows the quest is completed but no check mark on the objective of telling Phillip the Khans will allow them to join. Also, the vault is empty and I can't find Phillip and his crew at Red Rock Canyon