Most Indians - especially Punjabis - are well aware of the existence of a large-sized subset of the Sikh population which is extreme, fundamentalist, radicalized and separatist. The Emperor Kanishka terrorist act of 1985 was a direct result of this subset, as have been numerous other large and small incidents (also see this, this, this, this, and this). Any regulation that relaxes security-checking for the turban opens up a potential security hole, especially since the turban is frequently large-enough to accommodate a small-sized bomb/weapon (large enough to bring down a commercial airliner).
And so, in my opinion, the turban - irrespective of which religion's individual wears it - must undergo routine/stringent security checks at all airports worldwide. Strong and loud voices by Sikhs that touching the turban is an insult should not deter the airport security agencies from thoroughly searching it. Religious sentiments of some cannot be allowed to come in the way of the safety and security of the public.
I, for one, want to feel 100% safe whenever I board an aircraft, no matter how much inconvenience it causes to me or to others. We can certainly do without another Emperor Kanishka.