Alright, here again after years of being lost in interstellar space. And I have some speculations about this all.
First: There is a third entity that has access to a long gun - the puny-pronoun-hating LOTA. LOTA's motives have always been a bit inscrutable to the Toughs and even Petey. Petey at some point offered LOTA "asylum" in the Fleetmind, which LOTA refused on the basis of "being the only known check on Petey's power". Not saying LOTA had something to do with this, but it is possible.
Second: The target of the latest shot was not Maxim 39 itself, it was Srabben and/or the evidence of his piracy. Don't tell Chinook that, having her friends described as "collateral damage" would not be wise at the moment.
Third: Since we don't know exactly how this scenario came about and how a decision was made - all we know is that Chinook at some point questioned it and Petey insisted on "it has to be done right rather than well":
https://www.schlockmercenary.com/2017-10-18 So actually, yes, I would say Chinook has grounds for being angry at Petey here since it's obvious that it was his plan, and she didn't have to necessarily have rewritten her memories.
Fourth: Petey might have a motive and means - after all, with LAZ-5 gestalts, nobody is "dead", and everyone is merely "inconvenienced". So I wouldn't put it past him to put his friends in harm's way or even actively kill them if it advances his own plans; he can simply grow new copies and as far as he's concerned, that's the same to him, no harm was done.
In the end, I do hope that Putzho manages to somehow balance this situation properly in his capacity as the Ego - because the Superego seems to have just triggered the Id.