I don't think the world at large understands the mechanisms of how Eldians turn into titans. Marley has no reason to explain it, and even if they did, the danger they (Eldians) possess remains, so others may be wary and resentful of them as a people. Zeke was shown being able to shout out and create titans spontaneously (during the air drop in the first episode this season and off screen in season 2, unless you believe he individually held down and syringed Connie's whole village), so what if other Eldians can do that, or what if you don't know any better because you aren't privy to Marley's military secrets and just assume they can do that to themselves? I certainly believe they are rightfully afraid now theat they have struck the mainland.
Also, it would seem this entire conflict so far is of Erin's independent actions. He knew the scouts had to come get him, so he set up the stage to strike where he could accomplish the most of his goals (whatever those are/were; likely claiming the warhammer titan) before he is restrained by his own people.