tbh I don't see why good quality silk plants, for instance, shouldn't do the same job; the cardinals really only need them for cover and a sense of security. Even plastic plants, I'd have said cardinals are much less at risk from tearing than, say, a betta.
If it offends people's sense of aesthetics that's a different matter; I am personally a bit of a purist in my tanks, but have to recognise that my cories would be just as happy with a fluorescent skull as with my beautifully arranged bogwood cave. I'm sure your cardinals wouldn't feel hard done by if you got artificial plants. It is true that plants lower nitrate levels, but so (usually) do water changes.