In his book Time Reborn: From the Crisis in Physics to the Future of the Universe theoretical physicist Lee Smolin takes a shot at the anthropic principle. He is not in favor, because the principle supports cosmological theories (such as eternal inflation) that cannot be falsified by observations.
I think one can agree with the sentiment that theories should not just rest on a principle alone but still view the anthropic principle as self-evident. In any case, the following reasoning by Smolin for refuting the principle's role (in reasoning about the cosmological constant, but it could be X) seems flawed:
I’ll start with a fallacious argument that goes like this:
Galaxies are necessary for life. Otherwise stars would not form, and without stars there is no carbon and no energy to promote the emergence of complex structures, including life, on the surfaces of planets.
The universe is full of galaxies.
But the cosmological constant has to be smaller than the critical value if galaxies are to form.
Hence, the anthropic principle predicts that the cosmological constant must be smaller than the critical value.
Can you see the fallacy? Point no. 1 is true, but it plays no role in the logic of the argument. The real argument starts with point no. 2. The fact that the universe is filled with galaxies is evident from observations; it is irrelevant whether or not life would be possible without them. So the first point can be dropped from the argument without weakening the conclusion. But point no. 1 is the only place life is mentioned, so once it’s dropped, the anthropic principle plays no role.
I would argue that point no. 1 cannot be dropped because the anthropic principle (in point no. 4) is about "life": anthropic stands for "of or pertaining to mankind or humans, or the period of humanity's existence". Without human life (if the argument starts with point no. 2) there is no observation and nothing is "evident from observations".
So my question is this: is Smolin's argument indeed flawed or am I missing something?