The sales punk didn't like how he was treated, so he gets revenge by (threatening) to leverage his own personal network.
It's pretty unlikely this is some organized practice at Groupon.
Is the culture such that anything goes?
Are the systems that review performance of sales reps not catching up with this sort of behaviour?
Groupon allowed this to happen, and it's for Groupon to fix.
Firing the guy would be a knee jerk reaction that would not to me be the right one. Not firing him and doing nothing would be worse. The best answer is a blame-free full review of how this occurred, and how they can design their organisation and process to make it never occur again.
Sounds to me like it's a kid barely out of college who can't control his emotions and is having a pouty hissy fit. His emotional age obviously is not advanced enough to prepare him for sales.
If you want to blame anything, blame the culture (Web 2.0? SF? VC funded world?) that believes that younger is always better.
That said, if we were talking about hiring a node.js dev, and comparing a 22 year old vs. a 57 year old, would "I fail to see how this has anything to do with his age. There are great developers at all stages of life." be applicable as well? Or would it reasonable to make some generalizations while appreciating exceptions?
What might happen: front page of Reddit, followed by the guy being sacked shortly afterwards.