JMA asked:
explain why a civil war in any country should be avoided at all costs?
The first people to avoid a civil war are those who live within the boundaries of the nation-state. I expect we all know civil wars are rarely a "clean fight" and short.

It is not pre-ordained that neighbours and those beyond should intervene.

Syria I think is now a civil war, although the ratio of regime supporters, opponents, "fence-sitters" and others are not clear. I have yet to read anything that states external support for the fighting opponents will be decisive. History I would contend is replete with examples of external actors being sucked in, who discover with :boots on the ground" that it is a quagmire.