This is science. The whole point of research is that we don't know the answer.

The way it work is someone comes up with an idea, and then it gets fleshed out into a hypothesis, and then people come up with ways to try and prove it. It doesn't always work -- sometimes it turns out the hypothesis was incorrect, and sometimes we just don't know how to prove it. Doesn't mean we don't try.

And frankly it's the same with the philosopher's stone. Just because we know now have the hindsight that it was completely bonkers doesn't mean they shouldn't have tried at the time. This is how science advances.