Except, that's not the MO of all Primals and their followers, and EVEN AFTER this event, it is unclear it's the MO of the Qalyana and Lakshmi. Not all Primals are like Ifrit. Some act only in defense, like Titan - if it wasn't for the Lominsans constantly trampling over their treaties with the Kobolds, the Kobolds could be perfectly friendly and reasonable neighbors. Some prefer to keep to themselves - the Sylphs are xenophobic and isolationist, but they stay put in their chunk of the woods and rarely bother others, and Ramuh himself prefers not to be summoned due to the harm he causes.
Up until the conference, there was no reason to believe that Lakshmi and the Qalyana might not also be a beast tribe that could be reasoned with, one with which treaties could be established, and who could be convinced to respect boundaries. Even on her initial summoning, Lakshmi made no efforts to encourage her followers to go to war; she was content to stay put and grant her followers blissful fantasies. There was little or no conflict until we barged into their home and slew their Primal. After that show of force, it's not unreasonable to assume that the Qalyana would want to participate in the establishment of boundaries, to hash out when the Warrior of Light would be allowed to trample all over their sovereignty and when he/she would not (and Eorzean terms are generally pretty generous: don't summon your Primal, and we leave you be to do whatever you like).
At the conference, however, the Qalyana leader revealed that she held a grudge due to the loss of her daughter. She wasn't mindlessly summoning Lakshmi because Lakshmi demanded it of her, but because it was a tool of her revenge to do so. Now, that leader is dead, in yet another show of force. Whatever new leadership is chosen, they may be more willing to compromise, so it is STILL in the Alliance's best interests to negotiate with them. Yes, they will invite them in for tea as many times as it takes, because war is something the alliance would like to avoid.
Dealing with the Tempered is WAY more complicated than "they are tempered, therefore they cannot be trusted". Even if you can't trust a nation, you can coexist with them - it happens all the time in real life, as well.
Strangely, Koji Fox specifically came out and noted that the Lamia in Sastasha (Hard) are NOT transformed women, but escaped Allagan constructs. It was all discussed in this thread. Lore aficionados, including Anonymoose, found it all a bit hard to swallow, though.