To begin with, as you've noted, the primals are a "negative" force. Moreover, from the time Lyland defeated King Thordan, I've long pondered why the dying primal perceived the Warrior of Light as a shadowy, ominous presence.
This was when it struck me that, in the process of repeatedly "giving form" to the primal essences imprinted on his aether, Lyland may have unwittingly allowed the egi to deepen their taint on his life force. Recall that summoning is different from arcanima, in that an egi is summoned forth from the evoker's aether.

Originally Posted by
y'mhitra
…you must focus. Visualise the aether flowing through you, a vibrant current of energy transforming into living fire. Hold this image in your mind, and the raging heat of your life force shall spawn an egi wreathed in flames!
Had Lyland not experimented with summoning, perhaps the taint on his life force would not have coalesced into the sentient beings that have to be forcibly tamed before they would accept an evoker's commands. The egi may obey him, but he can sense that they're constantly gnawing away at his consciousness, in a neverending attempt to reassert control.
Neither he nor Y'mhitra could have forseen what summoning truly entailed. Lyland was inspired by Y'mhitra's belief that resurrecting the ancient Allagan art might well give them "the power to bring this age of conflict to an end". He truly believed at the time that summoning would be a force for good.
But he later witnessed the horrors of what the Allag did with Bahamut, and experienced at first-hand the megalomania of the last Emperor, Xande. His belief in the Allag was thus shattered forever, redeemed only slightly by G'raha's sacrifice. The further horrors of Azys Lla only served to deepen his disillusionment with Allagan magic and technology.
By the time Y'mhitra related the doomed history of Allag's summoners, Lyland was already about to abandon the art. Unfortunately, although he had defeated Lahabrea in the aetherochemical facility, the Paragon's minions remained, and they remained determined as ever to provoke the beast tribes into ever more summonings.
Y'mhitra and Lyland were thus forced to tap the Dreadwyrm trance to permanently destroy the lesser Ascians. It was to be a pyhrric victory, however, because tapping Bahamut's latent aether had further worsened the primal taint on Lyland's soul. He could sense he was on the brink of falling into the madness that also claimed the ancient summoners of Allag.
The stop-gap solution came, ironically, from a return to arcanima. Thanks to Ardashir of Thavnair and Ulan of the Far East, Lyland was able to artificially create an entirely new class of arcane entity: the anima.
Housed in Lyland's newly designed relic, the anima now serves as a filter on his aether. It helps to regulate the primal taint on his life force, as he channels his aether through the relic to evoke his spells.
In the meantime, Y'mhitra has continued her research into a permanent solution to the primal crisis. There are no concrete solutions as yet but, intuitively, Lyland senses that it will require some means of pacifying the rage of the egi within him. Otherwise, the cycle of hatred and reprisal will only continue.
War is inevitable, yet it is war itself that frightens the beast tribes and spurs them into ever more primal summonings. And the more primals he slays, the more Lyland gets doused in their aether, and the harder he'll have to fight to maintain his aetherial integrity.