If you're with a bad adc, try and guide them. Remember that the title of your role is "support" and that it can translate to a lot more than just setting up kills. ADCs have the weakest early game, that's why they have a role specifically geared to help them survive it. If I'm with a meh ADC, I'll start weakening creeps so that they have easier last hits. I'll tell him to just focus on farming while I focus on zoning the enemies away from their own last hits, or poking them so they're scared to move up too far.
Stay with them and do everything you can until the first turret is lost. After that, the lane is done and you can roam wherever you please. But until your turret falls, it can still help you net kills if the enemy gets too cocky, and if nothing else can hold them at bay with smart plays on your part until allies can come down when they're trying to push for it, or are already going at it.
The offense here isn't that you left the lane. It's /why/ you left it that's toxic. You gave up on a lane that was still technically standing, one that could be saved if your mid or jungler came down to help even if your ADC was trash, and because of that gave your enemies a field advantage, a gold advantage, and reduced your team's defensive line by a third, and gave them an easy access point into your jungle. They can then proceed to gain full vision of that quarter of the jungle, which then puts your jungler in a rougher place. They'll fall behind in farm, possibly get killed trying to catch up, and when they have control of part of your jungle, your midlaner is no longer safe either. The enemy gains three more avenues to come in on your midlaner through that part of your jungle. That much pressure being put on mid and bottom will make your top have to leave their lane to try and save the other two and help out where there will inevitably be pushes at the weakpoints you have created, which leaves the top lane then open to be rotated to and the first or even second turret taken on a solid push.
Because you got too annoyed to stick with it, and forgot that your job is to support the entire team by holding the line as best you can, you weakened your entire team and gave up control on half of your side of the map.
THAT is the offense.
How can you expect Riot to determine if whether or not you've left lane was to grief your team or in an attempt to win? Is it based off of how many of your teammates rage at you/report you for it at the end of the game? It's a bit of a ridiculous thing to have seen Riot staff claim was a major part of why someone was banned.
And, again, is it Riot's job here to reinforce the meta? Because a support doesn't want to babysit a bad player, telling him what items to buy, how to position, etc (which, by the way, usually makes players angry) and, instead, wants decides to roam the map that allows them to be potentially banned?
League of Legends is an action/strategy video game, not a psychological game. Yes, a good player will help his teammate succeed and boost their moral.. but it shouldn't be a requirement. If someone is playing horribly I should be able to say "hey bro you're not doing very well, I'm going to go help a lane that knows what they're doing" without facing a ban.
