There isn't a rule that while you're eating at a restaurant that I cannot come over and fart on your entrée. (1)
No written laws on that one, never taught that was wrong in school, it is just one of those good manners things.
Can you produce a signed document where I pledged to not do that?
No paper work?
Oh...okay, so it's a go?
You don't actually live your life as if you have to have a signed agreement for every interaction.
That is because you inherently understand that there is an implied agreement - that implied agreements are the norm actually - and the implied agreement of those PvE groups is blisteringly obvious.
Unless, upon farting on your steak you'd take the excuse "well, we have no written agreement" as suitable?
No?
I didn't think so.
NOTES
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1: Thank you Big Trouble.