It's already the case that many contractual terms will be considered invalid even if both parties agree. In the EU, there are also -- especially for B2C contracts -- a number of terms that are implied and can't be waived.

Examples include distance selling regulations (that provide the right of withdrawal) and limitations on what's considered an acceptable mid-contract price increase. GDPR adds extra restrictions on what privacy rights businesses are allowed to require consumers to opt out of.

So if you've done it correctly, the customer isn't rejecting your terms: they're exercising their options under the contract you've offered them.