It depends on what cruise line you are taking and what knife you attempt to bring.
It's easy to make sweeping generalizations, but the truth is, if you are comparing a bad cruise experience to a discount store, it sounds like you selected the wrong one for your taste. Imagine if people did the same for knives based on a Jarbenza experience...(all knives are garbage, blah blah blah!)
If the cruise line you are using says no knife, no way, no how, chances are they mean it. I would still slip a small unassuming folder in my pocket and hope for the best. They may tag it and lock it up for me, but last time I went, no one said a word. That said, if anyone would have asked, I would have been totally honest.
It really came in handy for sharpening pencils and cutting off tags from items we purchased.