Devils Advocate
I'm going to put aside the issues of whether WLM should be where it is, whether it's justified in having all that airspace and how restricted access is or should be. Lets just assume that it's justified (or if you can't accept that, accept that it is the status quo for now). I don't think anyone can deny the RAAF the right to control their airspace and make it not available when they need to.
By preventing flight planning via WLM may actually increase safety! (what the.....?) Every VFR or low level IFR/NVFR pilot knows (or should know) that they need to plan elsewhere. If, once airborne, they get a clearance (90% of the time has been quoted) then great. If not, then they should have a plan 'b' ready to be executed without increasing stress levels (which for NVFR or IFR in a single needs very careful thinking about).
If flight planning via WLM were allowed, everyone would do it and consequentially each time (10%?) clearance was refused then you have a pilot who may not have a plan 'b'. That pilot then finds themselves over tiger country at night, in cloud whilst unprepared and needing to exercise command judgement, deal with weather, passengers, failures etc. Its much much harder to turn around and go back than to not take off in the first place.
By preventing the filing through the RAAF airspace, a little (lot?) of risk minimisation is essentially enforced upon pilots as they should then consider if they, their aircraft, the weather etc is actually suitable for the route they may end up flying - via tiger country.
Dick talks about a possible 1 in 50 year event. How many flights in the last 50 years haven't departed YBCG for YSBK because the pilot looked at the route needed to go around WLM and decided to wait for more favourable conditions?