This is a bold statement.
I'll agree that an experienced hobbyist who's familiar with their set up, generally, has no real need for a test kit. I very rarely use mine, so we're on the same page in that regard.
But a newbie, just coming into the hobby, who is trying to find their feet, a test kit is an absolute must. It is possibly the number one piece of kit they need to keep tabs on their system until, like us, they become familiar with the complex processes which go in in an aquarium.
Even guys such as us who don't test much mustn't become complacent. A good example of this is that as fish grow, over time, the bio load increases gradually, especially, if like me, you have a big tank with lots of growing fish. I like to keep tabs once in a while, just for peace of mind, so I can check that my water change schedule is adequate for my ever increasing nitrate creep.