I'm pretty sure what is described in the above blog post (confiscation of unlabelled optical media from LRT/MRT commuters) is obviously stupid, though probably not illegal. The rail authorities can probably refuse entry to anyone for any reason they consider valid.
It's probably legal, but I doubt it's enforceable though. Anyone who's ridden the MRT during rush hours knows what I'm talking about. Security inspections last roughly half a second for every three passengers; the security personnel will simply make a quick pass through your bags with their stick. Any containers inside the one inspected are let through easily. In fact, even though I ride the MRT nearly everyday , I've never encountered anyone being turned away because of what they were carrying.
I've lost count of the number of times I've premeditated how easy it would be to sneak some sort of undesirable element into an MRT station. I ride the MRT every day knowing full well that any half-hearted troublemaker could easily put my life in peril. Riding the MRT is probably only marginally safer than duking it out with the buses on EDSA.
Mall security is even worse, those inspections done by security guards at mall entrances are a waste of time. At least the MRT guys have the excuse that they have to deal with droves of people at a time; There are mall entrances where they barely glance at your stuff in a routine manner; you could be sneaking in a decapitated human head in a plastic bag and they wouldn't notice. The only criminals that would be stopped by these half-hearted measures are the stupid ones. The smart (hence dangerous) ones would easily breeze through.
Not that I want the hassle of through security checks mind you. It's just that the current practices seem pretty much a waste of time, when these inspections are just to show the public that MRTs/Malls are "safe."
Edit 14/Feb: BoingBoing has picked up on this.
 except when I'm lazy and decide to take a cab