The toxicity starting to happen.

[jameseoakes]

There's a fundamental difference in motivation that's important to understand (This is not an endorsement of pulling as a DPS.);

A DPS that pulls extra mobs is doing so in 99% of cases because they genuinely think the group can do better, and that doing so will make the run more efficient and save themselves time. Although misguided and possibly selfish, they aren't intentionally trying to hurt anyone (usually).

A Tank that intentionally lets someone who pulled die is doing so out of malice, with the explicit intent of hurting another player as a 'punishment', with the known outcome of decreased party efficiency.

Still don't see why the tank is the villain in this, he made a call on what was a sensible pull if the party is not happy about this they can talk about it after the pull. The DPS going and get those mobs is griefing and and fall out from it rests on him.