I think that in case of a debit card it's not that big of an issue, you buy a product with a crypto, the seller receives fiat-currency. The holder of the card obviously wants to spend crypto even though the price might go up right after he spent them.
In my opinion it's better to change all fiat you are going to spend anyway into crypto, put them in debit-card wallet, after a month or so you will already buy more with it then if you would have kept it in fiat.