What I was thinking off, Vestal, was more the way English case-law works. For instance, with marital rape in 1992, the law wasn't actually changed - there was a crucial judgement by the law lords (as was then - I think their role has now been taken over by the supreme court) which explicitly stated that the prior interpretation of the law (Hale's dictum from the 18th century) was outdated. The law commission report is here.
As I understand it (this is where we need Lass - though she's a lawyer in Scotland where the law was already sensible), the law commision was (circa 1990) looking into getting rid of the common law presumption that a husband could not rape his wife, when that was overtaken by case law, and in particular the judgement of the law lords - see section 1.4 (can't copy and paste as the pdf is a scanned copy of a print document.)
I think what's gone wrong here is that the law already clearly allows for divorce on the basis of "unreasonable behaviour" (it's what my mother used to divorce her first husband way back in 1956), but that this particular judge has a totally screwed idea of just how unreasonable behaviour has to be in order to constitute unreasonable.
Also, as I understand it, after 5 years even if the divorce is contested, you can still just walk away - it's just a much longer time. I totally agree though, it should be the case that you should be able to say "this isn't working for me" and get a divorce in a minimal amount of time, regardless of what your spouse says. ("This isn't working for me" of course doesn't absolve you of financial responsibilities regarding division of the assets, child maintenance, etc.)
But it's not immediately obvious from this case that the law needs changed - the law may be okay, but this judge may have applied it wrongly.