If you're on someone else's property, of course you have to follow their instructions. I'm not advocating breaking the law by trespassing per se. There's a difference between standing up for your rights and breaking the law. There's no point going to jail or paying a fine for photography. However, I doubt the police are going to come for every complaint made regarding unauthorised photography. And as Vince123123 said, if they manhandle you, they may be committing offences themselves. That said, one should be smart about it-- if someone breaks your bones or your head, your rights are no longer important.
But if you're on public property, they can't do anything to you. Your example proves the rule-- they didn't arrest you, did they? No one can fault the police for being extra cautious in this day and age, but they did make it clear they did not have the right to stop you from making a phone call, just that they were doing their job in checking all suspicious characters.
Is there a law against taking pix of sensitive installations, such as military facilities, etc? I don't think so, but I think anyone who does so will certainly be "invited" to tea with the men in white, even if they stand on a public road to do so. Lets not be stupid in trying to stand up for photographers rights. Even if there is no specific law, there is ISA in Singapore, that's something which most free societies don't have, but that's another story for another time.
Just finish a full day shoot and only see this now.
My post quoting you was just a caution note to newbies here who may get the wrong impression. You did afterall posted that:
It's not that difficult if you stand your ground. I doubt they will manhandle you. And most security "guards" in Singapore are not armed. You don't have to explain your actions to anyone, esp. if you're in a public place.
Going by your later posting, you do seem to agreed with me that on private property, you do have to follow the rules there hence having to explain your actions if you do break their rules ( if they said no photography and you shoot, you have to explain to them what you shoot and why ). On public property you need to explain your actions if the guys in blue ask you what you're shooting and you agreed that you may be having kopi with them if you were to shoot a military facilities, I'm very sure that if, on that day when I'm outside the police station, I'm pointing my camera towards the police, I'll be having an interview with them w/o the kopi :bsmilie
As a mamber of CS I just hope that newbies reading your post don't get the wrong impression that they can go around shooting anything they like and they don't have to explain their actions to anyone, esp. if they're on public property.