In general, I support the idea that a medical (i.e. scientific) claim should be supported by objectively verifiable (or falsifiable) evidence, and that claiming some nostrum is bogus should not give rights to someone to declare open season on the critic - the normal laws applying to arguing whether something is true on a balance of reason, should suffice - whereas libel law quite clearly reverses the burden of proof in a weird way
however, I think there's another, stronger reason that one should support simon singh against the chiropracters (well, specifically, the British Chiropractic Association):-
unsupported medical claims endanger lives. there's a process which has a bunch of checks and balances for deciding which therapies are appropoved - sure, there are complimentary therapies (mostly they have some sort of value if you believe in them), but there are serious problems claiming a therapy will address something (e.g. asthma) which can have deadly consequences, when there are mainstream medical producedures which have efficacy, nd yo umight take attention away from them.
I would claim that false claims about an alternative treatment, just as false claims against an established treatment (e.g. MMR) are actually a crime, since they are effectively 1. appropriating medical expertise which the claimants don't have (this is a crime in the UK) 2. could be construed as criminally negligent, if they do not position the claim correctly in the ranking normally afforded to different current scientific theories
so aside from the possibility the Judge has made a mistake technicall in the current finding (that is being appealed) AND aside from establishing a new set of legal stuff in and around science, I think one could counter sue the BCA for risking peoples' lives - I am not a lawyer, but last time I looked at something similar, I asked a lawyer and was told that this was in principle do-able.
see sense about science for the background and lots of details.
usefully primary source is the article, annotated with primary sources and the BCA's press releases
Note that wikipedia's entry on Chiropractic clearly claims it is "not based on solid science."
So is the BCA going to sue wikipedia too?