>>96242075 (OP)
While there's nothing wrong with that from a moral perspective, a huge issue is that TCG often designed with rarity and pricing being a sort of meta balancer.
Essentially, it does stop a lot of people from having ridiculous decks everywhere but the most competitive play because it would cost a small fortune to build them.
At the same time being limited to shit you find and having to make the best use of it is also fun but that's only viable as long as people you play against also have limited choices.
The issue is that once you allow Proxies, it will result in everyone running the most no fun allowed optimized decks because even just one person doing it would inevitably start an arms race because the only way to play against a deck like that is to also use proxies to have a deck with fucked up combos, when it's free to escalate the arms race nobody will ever stop. Also it makes cheating easier to pull off, since anyone can just have a card with slightly edited effects, more favorable wording etc.
That all said, if the game's balance is completely fucked the moment every card becomes free, then the fault lies with the developers intentionally designing a shit game to squeeze out as much money as possible and not with the players. But that's the point, TCG are designed in a way where money breaks the game on purpose so if you want to beat someone solely in a contest of skill then play literally anything else.