Criticism: Anarchism can't provide defense against invaders.

For defense against invaders, there is:

• Militia - local, defense-only, non-standing army
• Large insurance firms or corporations (and consortiums of such) who have a lot to lose
• guerrilla warfare

There are factors which make attacking stateless areas less likely or more costly than attacking states:

• Free-trade makes invasion less likely than under statist regimes, where protectionism is commonplace.
• Without a State apparatus, anarchist societies are harder to hold - no existing authorities to co-opt.
• No statist standing armies to fear.
• Undermining of "us" vs. "them" propaganda, i.e. no unified fearsome "them."
• No tax-base for competing states to fear.
• Not land-based, so WMDs are impractical.