Using an API key is orders of magnitude more expensive. That's the difference here. The Claude Code subscriptions are being heavily subsidized by Anthropic, which is why people want to use their subscriptions in everything else.

The people mad about this feel they are entitled to the heavily subsidized usage in any context they want, not in the context explicitly allowed by the subsidizer.

It's kind of like a new restaurant started handing out coupons for "90% off", wanting to attract diners to the restaurant, customers started coming in and ordering bulk meals then immediately packaging them in tupperware containers and taking it home (violating the spirit of the arrangement, even if not the letter of the arrangement), so the restaurant changed the terms on the discount to say "limited to in-store consumption only, not eligible for take-home meals", and instead of still being grateful that they're getting food for 90% off, the cheapskate customers are getting angry that they're no longer allowed to exploit the massive subsidy however they want.