1. Would high level experienced tanks selling their services be spending the same amount of time running dungeon roulettes for free? The answer is no, so that means that if people are doing runs for money, those are runs that otherwise wouldn't have happened. You may have 1000 DPS waiting in queue for 100 tanks. If 10 more tanks do runs for gil, then now it is 1000-110 instead of 1000-100. That eases the queue on everyone who steps in line after the DPS who paid a tank instead of queuing. You may not like it, but the queues are better off for their involvement.

2. There are a lot of bad arguments about how this is robbing people. It is not. People can use the DF for free. Tanks who want to roulette to help strangers or queue their friends can do so. Some tanks value their time and don't feel an obligation to endlessly run content low level content that is not sufficiently rewarding for a mob of entitled Ninjas.

I have a lvl 45 paladin and there are plenty of things I would rather do than ease the low level ninja queues. I don't sell my services, but I also don't go around running roulettes out of the kindness of my heart as people seem to be expecting tanks to do. I'll run stuff for my friends or FC mates, but if a stranger wants me to tank dungeons for them because the queues are ridiculous, they had better offer me something worth my time or I'll simply say no.