I've to admit that I don't think that I can claim to have made some significant improvements for all of humanity so far..
Every person on the planet needs to be entertained, and since there is someone out there who does make significant contributions to society that does like Starcraft enough to watch a documentary about a popular team, it must have some inherent amount of worth.
Being an entertainer isn't the same thing as curing cancer or engineering a cease-fire between warring nations, but it doesn't have to be.
Whereas pro starcraft almost seems to promote the opposite.
I'm sure that some SC players do work out, but for every player who does I imagine there are hundreds where their time playing video games eats into time that they may have otherwise spent exercising.
I have a stereotypically productive job, and I'm good at it (and enjoy it). Nothing spectacular, but you probably wouldn't sneer at it either. The reality is that I almost certainly bring less useful value to people's lives than a really good quality entertainer.