So long as Australian crossings only have booms over the entry side there will be half of the possible approach routes unguarded. That style of crossing is not permitted in some other countries or at least not in suburban areas.
I don't advocate religiously fencing our rail lines in all areas as is done in, for example, the UK simply because we have no need to protect anyone from anything in the vast and largely uninhabited distances of the outback.
Lineside fencing is being installed on the suburban routes at a rate of knots already so while there are still substantial unfenced lengths, including on the Frankston line, those might not remain so for too much longer.
Level crossings with full booms, where those faced by approaching traffic fall a few seconds before those on the "exit' side, give far more protection but require CCTV supervision to ensure no-one becomes trapped. Under normal operation they never should - this is purely an additional safety feature.
Ultimately we may never protect the foolish and downright stupid from themselves. We can take all reasonable measures based upon the assessed level of risk but when you consider that even high-security jails are occasionally broken out of then it seems nothing will stop someone who is truly determined.
Whether the incident at Skye Road could have been prevented by full booms is something the enquiry might need to look at. However it was caused - and it appears it may have been a tragic accident - all accidents are caused somehow. There is never a no-blame scenario.