I think that it's perhaps the nature of those who summon the primals that give rise to whatever personality they gain.
From what we know of King Mog, he was a benevolent king to his moogles in his legend, yet when summoned, he was more evil, most likely a twisted version of what he used to be.

From what I understand in the King Mog quest, the primals are summoned from the wishing power of the collective mind and giving form through the use of all the crystals gathered.
Since most of the time they are summoned for protection, they are thus given the personality of one who wishes to smite his enemies and conquer others.

My theory is that if the good faction of say the Amalj'aa were to summon Ifrit, perhaps he would be more benevolent.
Of course, due to the use of aether, they would probably never do that.


Anyway, I learned from reading Anymoose's resume of 1.0 that the ritual to summon the 12 during the battle against Bahamut was akin to a primal summoning. Since the ritual needed the prayers of the people in order to appear, this itself was destructive to the world due to the high amount of aether needed.