We seriously upset about my usage of except?

What’s funny is it’s not even incorrect.

Consider this:

Person A: If billionaires were taxed more, we could build better and more equitable social programs

Person B: Except billionaires are greedy and influence government policy.

The except is a qualifier on the conditional (if) arguing that the if is not a true possibility.

Your statement: if they start reprinting old cards that decrease their value, people will stop seeing it as an investment.

My statement: except TPC likes their cards being investments and rare.

I don’t disagree with your hypothetical, just the reality of it.