Instead of government using its resources to provide protection for the threatened party, perhaps it should use its resources to eliminate those who make the threats. A two-armed approach would be required: (1) legislation that prohibits threats of the sort we are discussing here (which probably already is on the books) and (2) determined efforts to find, prosecute, and imprison those who are guilty of making such threats (which is surely not being done, even when such laws exist). A clear distinction must be made between acceptable and unacceptable forms of speech, without religious dispensation granted to those who, for example, threaten Hirsi Ali and Salman Rushdie and succeeded in killing Theo van Gogh.

It seems that these governments have very little interest in eliminating the threat by finding and prosecuting those who make threats, and they instead place all blame on the victims. Eliminating this problem would, of course, require the recognition that we are in a war against a violent culture and an abandonment of the politically correct and multicultural attitudes that make government unwilling or unable to fight a culture that has such unacceptable standards. No hope of that happening.

That helps explain why, in 2006, the Dutch government tried to revoke Hirsi Ali’s citizenship over an old immigration controversy

The move to revoke Hirsi Ali's citizenship came shortly after a Zembla expose that publicly revealed the circumstances of her immigration. The controversy about her immigration papers was not about the false name as some suggest but that she applied for asylum stating that she had come directly from Somalia where she faced persecution rather than by way of Kenya, then Germany where she did not face immediate danger. Her political allies made sure she did not lose her citizenship.
This controversy was compounded by her stand in the Taida Pasic case where an 18 year old Kosovan refugee was deported months before she was to graduate high school due to iregularities in her immigration paperwork.

Last week, the Dutch government abruptly cut off her security funding, forcing her to return briefly to Holland.

She was given warning. The Dutch government payed for round the clock security including 6 guards, secure car and house at a cost of several millions of euro per year. This security continued to be payed for a full year after she moved her permanent residence to the US. If she moves back the Netherlands she will continue to receive security regardless of some bellyaching. I don't think it reasonable to expect the Dutch government to continue to pay for her security indefinitely if she is not a resident. At some point either the American government, AEI, or she should pick up the tab.

Where does one draw the line?

Well in this case , it seems the Dutch government drew the line when Hirsi Ali decided to take up permanent residence in another country.

I really don't see why the Dutch government should be obliged to pay for the protection for someone who
has decided to live (and pay taxes) somewhere else.