I've pretty much always proxied over the years and am still proxying some cards in my decks, although at this point it's mostly just lands. I'm lucky my LGS group doesn't mind and we waver on the 75% line (sometimes we slack off, sometimes we tilt a bit too close to cEDH for comfort).
In fairness, my LGS knows of decades-long plan to eventually foil out my (eight) decks and since I wish to spend minimal time trading on-and-off (it's supposed to be a hobby after all) I don't buy nonfoils, only foils directly (my first decade in the game already provides me supply I've been slow to reduce already and the occasional prerelease / pack therapy doesn't help), so they know I'm basically "camping" in the secondary market to snipe foils when they're around their lowest.
Fortunately I sit now on a sizable collection that I could afford to not use proxies for nonlands at the cost of some power-level, so whether I proxy nonlands is pretty much meta-dependent. When Eternal Masters introduced
Mana Crypt arms races, I had them proxied so I could catch up, but since it more or less "died out", I took them out (man it was one of the more uncomfortable proxies I felt I had since I never owned one).
Lands I stay stubborn on because generally speaking even on the lower-end of our 75% meta, most of us keep out landbases smooth all the time, so shelling out for foil
Temples I would consider a waste of money in the long run. I could use basics, but I also aesthetically have them foiled with the same art, so if I don't have spares of the same (not all of them are easily acquired), I'd rather stare at 8 foil Plains/Islands and a proxied
Skycloud Expanse than 8 foils and a out-of-place basic.
Sticking with the policy, I do not proxy cards that cannot be foiled (so basically Commander precons don't exist to me outside of 12-15 cards) and cards on the Reserved List (including ABUR duals). I did for a brief moment include RL cards with foils but seeing the price spikes over the years I was convinced I was never getting another one (I bought a foil
Palinchron years ago), so the entire List got binned.
If a card looks like a prime reprint target and has inflated considerably due to supply drying up I generally just proxy and wait it out for the reprint. The foil usually costs ridiculous sums for a reprintable card and buying the nonfoil is just throwing money down the drain when the reprint hits. My favorite example of a card like this is
Hall of the Bandit Lord (although ironically for that card I do have a nonfoil, so I just use it instead, but boy would it crash like crazy if it was reprinted again). That being said, my perception/policy comes because I do own some of such cards myself (nonfoil though) and seeing how hard it is to offload them myself until reprint drops its value, buying them seeing doubly foolish. I only do that on the rare occasions I can see myself shifting off the cards (I think spent nearly $40 on a foil
Oracle of Mul Daya a few years ago, but months after that I sold off my two nonfoils to compensate for that sum spent, it'd be the same thing today, except riskier since it'd be harder to sell the nonfoils at their even crazier prices now).
As for my opinion on others using proxies, I'm no hypocrite, I'm fine with it (I think long ago I met a player who 100% proxied his deck including basics). I did not run into one (the 100% proxy player was very casual), but if someone did a majority proxy to pubstomp, it's the pubstomping that needs to be addressed, not the proxying, although the proxying-factor does assist in addressing the issue.
I usually warn people of my proxies (and I usually play with the same regular group at the LGS, so most of them know anyway), I don't actually remember anyone being vehemently against it... usually it's the other way round, people are impressed by the "expensive (now)" bling I have (which I sniped years ago when they were lower / at their lowest and also probably mitigated by me having nonfoils to indirectly trade for it), then they get treated to my basic explanation of why I proxy (hence making the deck look like some frankenstein of expensive foils and proxies) and wait to snipe cards to minimize the cost of this hobby while still blinging it out and that they can do the same as well.