It seems to me that metaphysics questions are allowed, but tagging them as such sparks protests.
This practice seems inconsistent to me. I will re-tag the questions with a metaphysics tag if there are no better proposals.
The questions I mean to tag are those
About anthropic principle, fine tuning, possible worlds and existence of things without an observer. This includes hypotheses about quantum immortality and alike
About general properties of time, determinism/indeterminism, existence of the present, past, future, causality loops and eternity of the universe
About self-reference in measurement theory, existence of universally-walid theories and subjective decoherence
About limits of applicability of scientific method.
UPDATE As there is certain confusion about what the definition, here is how metaphysics destinguished and related to physical sciences by Peter van Inwagen:
Another sort of aid in understanding what is meant by ‘metaphysics’ is provided by distinguishing metaphysics from the things it might be confused with. First, metaphysics must be distinguished from the most general and all-embracing of the physical sciences: cosmology and the physics of elementary particles. (...) These two ﬁelds of study have turned out to be closely connected and have, since the 1960s, produced results that are of the deepest signiﬁcance for metaphysics. Let us give the name “physical cosmology” to those scientiﬁc investigations that intimately involve both cosmology and the physics of elementary particles. Here is an example of the metaphysical sig- niﬁcance of physical cosmology. Physical cosmology seems to show that the phys- ical universe had a beginning in time (about fourteen thousand million years ago)—or at least that it does not have an inﬁnite past throughout which it has been much the same as it is now. If this is correct, all metaphysical speculations that pre- suppose an inﬁnite past during which the components of a universe much like the present universe have been eternally rearranging themselves—our second set of an- swers to our three metaphysical questions provides one important example of spec- ulations that make this presupposition—are incorrect. And this by itself is sufﬁcient to show the relevance of physical cosmology to metaphysics. But if physical cosmology is of the deepest signiﬁcance for metaphysics, it nevertheless does not and cannot answer all the questions metaphysics poses. For one thing, it cannot answer the question, Why does the World exist? (...) Physical cosmology, moreover, does not and cannot tell us whether the physical universe is all there is—whether there is more to the World than the physical universe. Scientists sometimes assert that the World is identical with the physical universe, as a famous astronomer, the late Carl Sagan, did in the opening words of his popular television series Cosmos, but the assertion is a metaphysical, not a scientiﬁc, assertion. It is certainly possible to argue that science will someday explain all observable phenomena and that one should therefore believe that the World is identical with the physical universe, since one should believe that nothing exists beyond those things science postulates in the course of giving its explanations. But this argument is—and any argument for the same conclusion will be—a metaphysical, not a scientiﬁc, argument.