UNP supported SLFP in 1971 to eradicate insurgency. But MR did not do the same in 1989 and he capitalized on that and went to Geneva, Human Rights Council(at that time) against killings to eradicate terrorism. That helped LTTE too. As govt was fighting two fronts at that time.
Lesson to learn
A traitor like MR , who championed HR but in power killed innocent unarmed people at Rathupaswala with GR's help. But people voted both to power.
UNP which supported SLFP to fight insurgents were also voted in 1977, but SLFP never reciprocated when the same situation arose in 1989. SLFP and now SLPF are opportunistic parties.