Those statements were more or less true at the time because the ideas were faulty. They were insufficiently developed and they lacked proper evidence.

Example: many people claim that early Greek philosophers discovered that the world is round and that the Earth orbits the sun. At the time their claims were backed by evidence that could easily be contradicted by alternative hypotheses based upon different assumptions. We have only been able develop those ideas sufficiently and acquire enough supporting evidence for them in very recent times.

Getting back to the tax on dumb ideas thing: I'm a firm believer that extraordinary claims require extraordinary ideas. Sure, that means that we will cling on to old ideas far longer than we should. But what's the alternative? The alternative is that every idea is put on equal footing. Can't prove that the Earth orbits the Sun or that the the Sun orbits the Earth? Well, maybe the planets orbit the sun while the Sun and Moon orbit the Earth. Why would anyone want a model that messy? Don't ask me, ask the guy that Kepler was working for. (Kepler was the guy who proved the heliocentric model proposed by Copernicus.) Or maybe someone would propose that the planets are doing a cha-cha. I mean, why not since we couldn't actually prove the other models until Newton gave us a mechanism and Kepler gave us a verifiable model.

Discarding dumb ideas is simply a coping mechanism that allows science and society function. It allows us to focus upon developing the contemporary ideas and continue making progress. If we ever acquire sufficient evidence to say we should be looking somewhere else, we maybe prove a couple of the dumb ideas that we discarded along the way. But I'll guarantee you that the dumb ideas that proved to be true is going to be a tiny fraction of the number of dumb ideas that would have confounded us if they were placed on equal footing with the old ideas.