Officially, you are only entitled to ask them to leave or to stay where they are while you call the police. By law, you can't even touch them or detain them (assault).
That is amazing. You have my sympathies for living amongst so many blissninnies. it sounds like a VERY good placed to be a criminal though.
Amazing as it is, the entitlement to self-defense and the bearing of arms essential thereto cannot be withdrawn through a legislative fiat in any common law jurisdiction such as the British Commonwealth or the U.S.A. The following case law is rooted in the Catholic doctrine of double effect as laid down by Augustine, Aquinas, and Grotius, and reflects the reasoning dating back to Lord Coleridge in the case of Regina v. Dudley & Stephens. It has been personally field tested in California. Doubtless its counterparts exist in New Zealand.
"The necessity defense is very limited and depends on the lack of a legal alternative to committing the crime. It excuses criminal conduct if it is justified by a need to avoid an imminent peril and there is no time to resort to the legal authorities or such resort would be futile." (People v. Beach (1987) 194 Cal.App.3d 955, 971.) "By definition, the necessity defense is founded upon public policy and provides a justification distinct from the elements required to prove the crime." (People v. Heath (1989) 207 Cal.App.3d 892, 900-901.) "Necessity does not negate any element of the crime, but represents a public policy decision not to punish such an individual despite proof of the crime." (Id. at p. 901.)
"To justify an instruction on the defense of necessity, a defendant must present evidence sufficient to establish that [she] violated the law (1) to prevent a significant and imminent evil, (2) with no reasonable legal alternative, (3) without creating a greater danger than the one avoided, (4) with a good faith belief that the criminal act was necessary to prevent the greater harm, (5) with such belief being objectively reasonable, and (6) under circumstances in which [she] did not substantially contribute to the emergency." (People v. Kearns (1997) 55 Cal.App.4th 1128, 1135.)
"We acknowledge that '[d]oubts as to the sufficiency of the evidence to warrant instructions should be resolved in favor of the accused.' (People v. Wilson (1967) 66 Cal.2d 749, 763 [59 Cal.Rptr. 156, 427 P.2d 820].)" People v. Patrick (1981) 126 Cal.App.3d 952
Notwithstanding the benefit of the doubt, the obvious disadvantage of this affirmative defense remains in subjecting the accused to the burden of presenting the evidence of necessity at trial.