This 'guy' is saying that you will somehow regret that your time as a CFI will be time that was wasted. Obviously I disagree with him as well.

Instructing builds good social and working skills you'll use everyday in interacting with CA's, FO's, FA's, the ramp, and CSA's. You learn to read and interpret people better, and adapt your style and approach to get the best out of them. You learn to be a manager and leader. Your decision making ability, conflict resolution skills, and critiquing ability increase. You become a more professional Pilot, no doubt, as a result of being an engaged and introspective CFI.

Good luck. Network!