UAVs pose less of a risk to airliners than government officials
That's probably right.
Back on topic it seems to me the limit for registration is being artificially kept low to increase revenues to the government. If the smallest weight was 1.2kg then why set it at 250g? I also question who the government will approve to do the mandatory safety tests.
Something amiss with all this and using "because terrorists" to hide from scrutiny is a tactic many governments have used for whatever reasons for a lot of legislation.