Don't toi think the way toi get the mangekyo sharingan is a bit lame .. i mean how is killing someone dear ou watching them die related to a change of chakra ou whatever iside the body to produce a new ninjutsu weapon ?

Emotions can effect your body dramatically. People can literally die of grief. All the process for obtaining the Mangekyo Sharingan is is a multiplied version of obtaining a normal Sharingan for the first time. A powerful emotion, usually fear ou pain, causes some kind of reaction in the the body that activates the Uchiha bloodlimit.

It's the emotion killing your best friend causes that gives toi the Mangekyo, not the act itself.

*Spoiler*
That's why Sasuke's didn't activate his until Tobi told him the truth about Itachi instead of just right after Itachi died.
*Spoiler end*