I already give my support.
Starting with 2.1:
The video clearly shows Arnold pulling a weapon in a public area, immediately shooting at Yoddo. This isn't a very realistic thing to do, especially considering that the Mayor is nearby. It's not possible to justify killing Yoddo in a public area.
2.5:
It negatively effects Yoddo's roleplaying experience when he is killed at random, simply due to being in war with another organization.
3.4:
There's 2 NPCs in the nearby vicinity that would hear the shots, several people, and even the mayor. As soon as shots are fired, the mayor will completely destroy his panic button, and SWAT will be there in 30 seconds. Arnold risked his life to the extreme.
(Possibly) 3.24:
Arnold may also possibly have figured out that Yoddo is in the Cacuzza simply by reading the name floating above his head. Unless he was given a picture of Yoddo, or Yoddo was pointed out, Arnold may have simply been using OOC information.
6.1:
As Yoddo stated, Arnold may have mainly done this due to their war against Cacuzza. However, how would Arnold know that Yoddo is in the Cacuzza? Unless directly told by someone that knows who Yoddo is, either using a picture, or even pointing him out, Arnold would not recognize Yoddo at all.
6.3:
Two NPCs were in the nearby vicinity, neither one was taken care of. Both would call the police immediately.