So let's say your friend smokes weed. You have absolutely have no problem with it. And you & your friend go out somewhere, and you two are driving back home now.
You're driving his car down a long stretch of road at night with your friend. He lights one up, but you don't smoke any, and he finishes smoking and flicks it out on the floor.
You're going 75 in a 55, and you get pulled over by a cop, but it's just a speeding ticket, right? Police pulls you over, notices the smell of the weed, searches the car, finds more pot, and arrests you and your friend for possession of an illegal substance.
Why did you get arrested? You didn't smoke the weed, right? Hell, it's not even your car. You're totally clean. But your friend had the weed. Ever heard of guilty by association?
Your Linkshell represents who you are, and who you like to hang out with. You have a choice to drop a linkshell and find another one.