Why is everyone against eren ? What are his plans again? i totally forgot can someone expl...

Just like what the King had threatened Marley in the past, he's gonna make the Titans in the wall flatten out the world outside of the Paradise Island with their feet.
The team are against his plan because he's also about to kill innocent eldians in Marley's land as well. Plus they don't wanted Eren to sacrificed his humanity just so that his friends can live.