Scepticism IS science
Answering some of the more dismissive remarks here, I'd suggest it's fine to be sceptical given that when you come down to it, that is the very essence of science: for every hypothesis there must ultimately be some solid evidence, testability and predictive power before it becomes a theory we can put some trust in. Cosmologists do seem to be willing to challenge each others' hypotheses: it's just that dark matter (and dark energy) are currently the least implausible models for explaining the universe's "missing" mass—and whatever is causing it still to expand. And we do have conceivable candidate particles for dark matter, such as neutrinos, though there may be others the Standard Model hasn't yet identified.
But yes, there are alternatives, even those considered a little outre like MOND. Seems to me it is quite right for scientists to offer their hypotheses and bash away at them to see what fits the observed facts and what doesn't. I confess I'm a teensy bit worried about "dark" - this and -that because of the lack of evidence and the obvious worry that it's a bit easy to say "And then we invent something to fill the gaps" ... but the fact that we can't prove it yet doesn't mean it ain't true.
And for anyone who's paying attention, we probably have a long road ahead, given that the universe of cosmology and physics generally is still beset by unsolved questions, curiosities and outright weirdness, whether it's entanglement, the Koide equation, proton decay (where is it?) or vacuum energy and the Cosmological Constant. Argument fuelled by healthy scepticism is necessary, as is the willingness to correct blunders.
Bear in mind, for just one example, that for some years in the late 30s it was believed that what we now call a muon (which is an elementary lepton, kinda chubby electron) was a meson (a two-quark hadron). This was a mistake and took time for science, by theory and experiment, to fix it. But it was fixed. Science is a healthy process, so let's keep the ideas and challenges flowing.
Biting the hand that feeds IT
