I started back in the 60's and fished a lot in the early 70's. The old timers generally weren't purists because before spinning tackle the fly rod was the way to fish light tackle, whether flies, lures, or even single salmon eggs. I had a dentist neighbor who belonged to private clubs and only fly fished with flies, but I didn't see that attitude in public waters. I remember tippets being poor quality so a 5x was considered ultralight. Of course that made trico (aka "caenis", aka "the curse") fishing a very tough game left to far superior fishermen like George Harvey.
Although snob feeling was always around to some degree, I think it came on stronger when spinning techniques became more efficient. I have been doing angler surveys this spring and one reason more fly fishermen fish special regs areas is that more than I would expect just cant stand to see spin fishermen - it just ruins their experience. Most special regs areas are artificials only, but are fished mainly by fly fishermen. If they see one spin guy I hear about it for days Of course, nearly all fly guys are fishing with indicators and heavily weighted nymphs or tippets.
One final thought. Back in the early 70's the hot light trout rod in my circles was the Fenwick 756 - the 7 1/2' 6 wt. When was the last time a 6 wt was considered light?