I have a tendency to dislike proxies because it makes it too easy for people to just use dual lands and "some of the more expensive cards". There's THOUSANDS of cards that can be used for commander, but as soon as you start having people go immediately to a duals and fetches manabase along with proxies 0 and 1 drop mana rocks, you start turning all of those real neat cards useless because they're just not powerful enough to keep up.

It's an unpopular opinion, but I tend to see it basically as using cheatcodes or trainer software in a PC game or save states on emulated console games.

It can have a way of destroying any understanding of balance in the game, rob you of any sense of real challenge and thus any real sense of accomplishment... and because it all comes so cheap and easy, it's frequently just disposable entertainment.

You're so much less invested that you're drastically less emotionally invested.

Yes, that may seem overly dramatic, but it's true- and unless you have some other major way of investing yourself other than financially, you'll probably the sort to just drift off in a few months/years and then complain about how awful, dumb and lame Magic is.