avon killed his best friend, who was simply trying to steer avon to a safer and more lucrative path. he drew unnecessary attention to his organization with his braindead obsession over marlo. stringer already told avon that marlo could keep the streets. they didn't need it anymore. they were already making money without the blocks. they had graduated beyond that, and avon was too dumb to see it. avon didn't have any intelligence or pride. he was just a glorified street thug who made it to where he was because of stringer's intelligence and shrewd navigation of street politics. yeah, stringer fukked up with clay davis, but that's to be expected of anyone who starts dealing with people you're not familiar with, especially a politician like that. but stringer still positioned the barksdale crew to do big things, and avon fukked it all up.
avon didn't try to save stringer. he was jealous of stringer. i've seen cats like avon before, dudes who see the smarter black man and start catching feelings because he's just a mindless ghetto hoodrat who doesn't have that intelligence. avon killed stringer partly because of built up resentment over string's abilities.
You make valid points however, you do not understand the street culture and ethics that was existing there. You are seeing things from purely Stringer Bell's perspective, who was an actual snake that was moving the Barksdale Organization to a place that Avon never approved of. It wasn't out of jealousy, that's HIS organization and he TRUSTED his right hand man to push it the way HE envisioned it and not the way Stringer wants it. Not only that, if anything Stringer is the worst character for a number of reasons; 1) None of this would of came down to this downfall to BEGIN with had it not been for mistakes and bad judgment by Stringer in season one! 2) But the hit out on D'angelo while fuccking his girl on the side, then initially hid the truth from Avon and that supposed to be your homie. 3) SNITCHED, absolutely SNITCHED to the police on Avon. Had Stringer not snitch on Avon, Avon would of won the war against Marlo, and things would of been back to normal. The shyt the police had was on Stringer Bell NOT Avon.
What you failed to realize and why Marlo reacted the way he reacted with the classic "My name is my NAME" quote, is that this has NOTHING to do with how much money you built, it's about your name and street status, it about passing on crime family tradition. D'angelo in season one even explained that when he realized he's don't have the stomach for it anymore. This was about maintaining generations passed on. Those corners MEANT something to Avon, not the money, not the drugs, but the real estate. The wanted to control the blocks and keep his name and power and most of all RESPECT. By the end of the day, but the end of the entire THE WIRE season run, Avon was STILL respected and was still looked upon as a street legend. They quickly forgotten WHO Marlo was and that was the ultimate failure in Marlo's eyes IN SPITE achieving EXACTLY what Stringer Bell was trying to do.