What a whining article
The whole article appears to be a whine about the use of a 4Kg 'projectile' used against a plane, but then concedes that a 1.2Kg drone holes a helicopter. From the article:
"The 250g lower weight limit for registration was, as far as can be divined from the study report, simply not tested; the lowest weight category picked was 1.2kg, and while that drone smashed through helicopter windscreens, it did not penetrate an A320 windscreen."
So unless you are happy with helicopters being vulnerable, the 4Kg object is irrelevant: drones need to be regulated at a weight at least below 1.2Kg.
I'm guessing none of us commentards know how resilient a helicopter window 'not certified for birdstrike' (as per the article) might be, but it sounds to me like they decided that any drone of a mass comparable to a bird like a gull or something could be dangerous if deliberately or negligently flown into the path of such a helicopter, and so are now requiring registration for such devices. This doesn't sound like either incompetence or a conspiracy to me.
Incidentally, having a 'kids toy' drone of my own, they don't weight anywhere near 250g until the kid concerned is a very rich kid indeed...