A commenter at another blog expresses the basic tenet of the materialist philosophy called positivism. By way of dismissing a biological theory with which he disagrees the commenter remarks that "If you can’t measure it and can’t define it clearly and straightforwardly, it’s not worth thinking about."
Although a lot of thinkers formerly adhered to the commenter's view in the last century, it has some serious, even fatal, difficulties. If it were widely adopted it’d certainly empty life of just about everything that makes human existence endurable. We’d have to acknowledge that thinking about things like love, beauty, justice, meaning, truth, good, God and a host of other matters, is just a waste of time, but it's a desiccated and shriveled view of life that renders topics like these meaningless.
A second problem with this claim is that it's self-refuting, for if it's true then it itself is not worth thinking about since there's no way to subject it to measurement or a clear, straightforward definition.
To be fair, perhaps the commenter meant to offer a criterion for legitimate scientific topics with his claim. Perhaps he was rather sloppy and really meant to say that unless a scientific theory or postulate is measurable and clearly definable it doesn't count as genuine science. Perhaps, but this would then exclude from science a host of assertions that scientists spend a lot of their time thinking about.
It would exclude, for example, every assertion about the origin of life (and even perhaps thinking about life itself), the origin of the cosmos, the evolutionary rise and transmission of behavior, the multiverse hypothesis, as well as axiomatic assumptions universally adopted by scientists like the principle of causality and the principle of uniformity (the idea that the universe is essentially homogenous throughout its extent). It would also make thinking about metaphysical naturalism a "waste of time" since metaphysical naturalism is itself difficult to define "clearly and straightforwardly".
In any case, it doesn't seem as if the positivist's claim that nothing which can't be "measured or clearly and straightforwardly defined is worth thinking about" has much practical value.