You're assuming the reason the opponent is ahead is from roaming, that's not what i'm talking about, and if that's how they get ahead, then no shit it's still the lane's fault.
If the opponent is ahead because of an early game teamfight, or a poorly executed gank onto them. Then the fault of the enemy getting further ahead, isn't on the laner. Thanks to how much the game snowballs, getting a sizable gold lead, gives an insurmountable lead.
E.g. Enemy ADC is 5/0, but our ADC is 0/1. Then chances are that they will continue to fall further behind in farm, and kills. As the game progresses due to lane pressure and higher kill potential of the lane. In this case however, this isn't due to the enemy ADC roaming. It's purely based on support deaths and an early team fight advantage given to the enemy ADC, created by the jungle over committing to a fight at dragon which brought both mid and bot lanes into the brawl. The result was the enemy ADC getting 3 kills, and the allies ADC dying receiving no kills.
Fast forward 20 minutes after no allied jungle ganks, the enemy ADC now has a cs lead, 8/2, and the allied ADC is 1/5.
There is no way to determine based on that score, if the allied ADC was playing reckless or got overwhelmed by the lead of the enemy lane or ganks.
What's even more irrational, is when allies expect the ADC to commit onto fights when at this kind of a disadvantage or make assumptions about how they played a fight, and then rage when they don't do those things.
There seems to be an assumption that despite,at best, half paying attention to the trades, that you have a better understanding of the champion's capabilities given the relevant circumstances, than the person who has been playing the game from the prospective of the champion in the circumstances.
If this 1/5 marksmen doesn't use their only mobility tool to attempt a kill on the moderately low health, but fed, enemy in a 1v1. Then you get angry at them for not doing so. You've made 2 assumptions. 1) That they have the damage to actually pull off that trade. 2) That the current situation of the 1v1 wasn't a result of them already using their mobility, thereby putting it on CD.