Taking Credit Card details is not a point of "principle" but rather one of "technical consideration".

It is perfectly permissible to take - and store - CC details via an online shop (even one using zencart)... As long as the technical infrastructure complies with PCI requirements.

If your server set-up complies with PCI, and you use appropriate SSL that is recognised as being sufficient for accumulating such information, then there is no argument for denying the use of CC modules that facilitate this process.

Additionally, there is nothing stopping you from taking CC details even if your system is not technically compliant, other than the consequences of a breach of security - and if you are happy to accept that risk, then go ahead.