The cladistic belief in a single tree of life is just as irrational as all other beliefs (in Gods and such things) are. If there indeed would have been such things, then our reality would not have been.
The problem with Gods is that if they created the world, then who created them. The problem with a single truth is its incompatibility with a changing reality. If there indeed had been a single truth, then why does the world not find peace in this truth? No, the truth is that reality is like a campfire around which we gather to express our opinions about it. Some sit to the right and some to the left, but no one can sit in the middle of it.
Instead, cladistics is nothing but good old race biology (inherited from the Nazi biologist Willi Hennig)..