No no one needs to justify what scope they want to use. If you want to put the Hubble telescope on your gun you are perfectly fine to do so.
as for Ericc, his .308 semi autos are mostly used for offhand shooting at targets 300 yard or less, for this 3.5x is more than plenty, and those few occasions Ericc has to reach to 800 with a 3.5x optic, again its good enough. With an all purpose field gun, Ericc believes the 3.5x ACOG to be the best.
also it is no secret, that when we get older we lose our vision.. We lose contrast and we lose the ability to see things at distance.. So for old guys that are blind and wears coke bottles for his everyday vision... He should get the best glass and highest mag possible to allow him to see his targets that are 50 yards away.