The cause for Port Arthur: a nutter with a gun. Solution: ban guns.
The cause for Martin Place, Paris, Melbourne stabbings, bombings in Yemen, abductions in Nigeria........Islam. Solution: stop the islamification of western countries.
Integrate or get the f@#$ out of the country. Go and live in a more suitable country like Pakistan or Indonesia or Saudi Arabia but get out of Australia, Britain, France, Belgium, Holland, Germany, Denmark etc.
Tell them to swap welfare for life in a proper muslim country where they can have multiple wives, death for homosexuals, stonings, honor killings, full blown sharia and all the other trappings of Islam.