I have been motivated to start this discussion, by virtue of being increasingly frustrated with what I consider to be the flawed manner in which most of the advocates of alternative theories approach their topic. The intent is to avoid discussion of any specific alternative theory, except perhaps as some specific point applies to the general topic, but rather to concentrate on what makes an alternative viewpoint, hypothesis or theory potentially viable, and what renders it hopeless.
I will start by saying that I have no sympathy for, and will not discuss, any claim that 'mainstream' scientists hold to their theories for any reason other than that they believe them to be correct. The idea that standard theories are maintained by some kind of social pressure, or the need to maintain some standard theory, in order to remain employed, is nonsense. If this is used as an argument to support any alternative hypothesis, then that hypothesis is doomed to fail.
Standard theories are standard for a reason: They work. One common argument presented by the proponents of alternative hypotheses is that the mainstream scientists have overlooked some obvious fact that only the alternative thinker can see. This may be true in some isolated cases (though none in fact that I personally know of), but is so exceptional that it is not a reliable point to make, and is usually easily refuted. The adherents to alternative views would be well advised, I think, not to take the approach that the flaws in the standard are 'obvious', as it is almost never true.
Perhaps the most common failing I have seen here, a failing I've seen in every thread I've participated in, is the failure to understand the reality of the mainstream theory that is being criticized. When Einstein 'overthrew' the Newtonian view of space & time by his theory of special relativity, he did so by first studying 'mainstream' physics in intense detail. Only when he understood the 'standard' theories as well as anyone could, did he introduce his new approach. That's one of the reasons that special relativity became the 'standard' as quickly as it did. Amongst the current crop of alternative cosmologists, Jayant Narlikar is a champion of the Quasi Steady State Cosmology that originated with Sir Fred Hoyle, and a proponent of non-cosmological quasar redshifts. But he has studied the 'standard' cosmology more deeply than most, and understands it very well. Despite a belief in non-cosmological redshifts, for instance, he nevertheless mastered the standard interpretation enough to write a detailed and well received book on it (Quasars and Active Galactic Nuclei, Ajit K. Kembhavi and Jayant Narlikar, Cambridge University Press, 1999). And, despite being an 'alternative' cosmologist, he wrote an excellent review of 'standard' cosmology (An Introduction to Cosmology, Jayant Vishnu Narlikar, Cambridge University Press, 3rd edition 2002). The point is that he, like Einstein, has made himself a strong expert in the theories that he wishes to contest. Now, most of the people who post here are unlikely to study a standard theory with that kind of depth, but that does not preclude learning enough about the standard theory to see if the perceived weaknesses are real or not.
Another failing I think I see is the reliance on 'indirect' methodology. Historical tales or anecdotal evidence has its place, but neither can replace direct experience. If we see for ourselves that certain physical systems behave in a quantifiable & predictable manner, then we can discount claims to the contrary that are not based on equally rigorous observation. I think it is a particularly weak approach to claim support for a modern, alternative scientific hypothesis, by virtue of ancient historical records, without proper quantification of the purpose & sources. For instance, scientists have made use of historical records of eclipses to study long term variations in Earth's rotation rate. But in those cases, they have specific data as to time & place for an eclipe observation. But even then, they use the total set in a statistical sense, and do not use records that are insufficiently detailed. On the other hand, turning ancient descriptions of celestial artifacts into claims that modern plasma physics is all wrong, is a flawed methodology, doomed to fail.
Personally, I have lost much of my desire to take part in various threads, mainly because I don't have the time to deal with the heavy influx of thoroughly uninformed criticisms of the mainstream, which often leads to the alternative adherents sticking to claims tnat have already been factually disproven.
I have no problem with original thinking, and encourage it. People should explore new & alternative ideas, but not to the extent of denying the obvious. Supporters of alternative claims should at least have a sufficient grasp of the basics of the mainstream theories to know what does & does not make sense (and you must realize that 'common' sense does not always apply in the empirical sciences, where specific solutions to specific problems always reign supreme).
So, have I missed other failings? Overstated my case? Agreement? Disagreement? What do Y'all think?