Obviously the performance of tor is reduced when traffic increases, but performance isn’t the goal, privacy is. Increasing the traffic of "normal" use cases (as opposed to those targeted by state-level opposition) improves privacy for the entire network.
I agree that using tor for all your video conferencing and streaming needs is probably irresponsible, possibly unethical, but the performance is likely to be so poor that it’s not a good use case anyway.
Using tor for everyday text chat (by real humans) is unlikely to have a negative performance impact, and it does provide more noise for attackers to sift through, so it could arguably improve privacy for those who need it most.