OP seems to think the website is racist. (?) I do not know how true that will be. Like you said there could be just some issues with your card or it's just not compatible with the site. You would need to check again but either way, this highlights how in times like this bitcoin really is the best option to pay online for less hassle.
Yes, that's not discriminatory. The banks would even want you to spend your card and purchase your things under your limit if it's a credit card.
Addressing the issue of rejected card and concluding that it is racist isn't actually enough. Everyone experiences this when there's a problem from the bank and we don't even conclude that we've faced racism.
But if it's about Bitcoin, we agree that it's open for everyone. And the transactions are irreversible so there is no room for mistakes per transfers.