'The Constitution Is Not A Suicide Pact'

Would someone please explain why this means:

that civil liberties only go so far, and at extremes, security must take precedence ?

I tried to reference a suicide pact and more context here, but I still don't see how to determine it.

I'm not politicking or legalising this; I ask only about meaning.

The phrase "The Constitution is not a suicide pact" contends that the civil rights guaranteed under a constitution (the U.S. Constitution specifically, but I suppose it could apply to any constitution) should not be construed in such a way as to enable the destruction of the society it governs.

While the general idea goes back hundreds of years, U.S. Supreme Court Justice Robert H. Jackson was the first to use the "suicide pact" language specifically, in his dissent in the 1949 case Terminiello v. Chicago, in which the majority ruled that a Chicago city ordinance banning speech that "stirs the public to anger, invites dispute, brings about a condition of unrest, or creates a disturbance" violated the First and Fourteenth Amendments to the Constitution. Dissenting, Justice Jackson wrote:

This Court has gone far toward accepting the doctrine that civil liberty means the removal of all restraints from these crowds and that all local attempts to maintain order are impairments of the liberty of the citizen. The choice is not between order and liberty. It is between liberty with order and anarchy without either. There is danger that, if the Court does not temper its doctrinaire logic with a little practical wisdom, it will convert the constitutional Bill of Rights into a suicide pact.

'The Constitution Is Not A Suicide Pact' is a common political phrase in the USA.

(Just to be clear, it's not "extremely common" like say "tea party" or something. But it's "quite common" -- for example, like saying "soccer mom" or "bleeding-heart liberal".)

It actually has a wikipedia page:

http://en.wikipedia.org/wiki/The_Constitution_is_not_a_suicide_pact

As you say, this sentence:

'The Constitution Is Not A Suicide Pact'

means exactly this:

'that civil liberties only go so far, and at extremes, security must take precedence?'

Quite simply, in the political context under discussion, "the constitution" stands broadly for civil liberties; the more laissez-faire side of the spectrum.

So in answer to your question why does A mean B, it's because in US politics "constitutionalism" is (typically) the more laissez-faire, civil-liberties side.