Sometimes, obeying your conscience requires sacrifice.
On the other hand, it's Girocard's responsibility to make their interface as easy-to-use as possible, and to market themselves to major online retailers, so that they become just another selection when using online retail. Maybe it's just a matter of time. However, that may be a long time.
I'm surprised that the major cryptocurrencies haven't been popping up as more common payment options. When you think internationally, the payment options popularly available are exceptionally limited. (Seven continents and almost 200 countries and there are.... maybe four or five worldwide payment options.) The virtual wallets like Google Wallet and Apple Pay have been making very slow progress lately, if any at all. And really, those online wallets are simply variations of the Paypal formula, so if you object to Paypal, you probably object to these alternate digital wallets as well.
With that said, most debit/cash cards that I am aware of can now be used as credit cards, as long as the balance meets or exceeds the amount being paid.. It's up to the bank to make it work right, and to avoid over-charges. I think I remember one of my friends being able to contact their bank to use a temporary credit card number in such a way that from the person's point of view, it was like making out an online check with a special 16-digit account number, and to the retailer, it looked like a conventional credit card.
As for objecting to using cash cards, it's just a financial tool. Objecting to using any cash card makes as much sense to me as objecting to using any hammer when faced with a nail. Now, I can certainly understand not using the tools made available by companies that have clearly demonstrated an anti-customer attitude, but other companies should be able to offer something that can compete. It sounds like European banks should work harder to provide alternate payment options that work like credit cards, specifically to enable more online payment options.