He was nearly killed because they thought he was coming to attack, so he believed that after explaining the situation they would have helped as fellow humans, unfortuantely is a pure isekai so people have their own morale, even if he is a human for them is a danger to be killed, or used as battery, I'm a bit sad for the demons we see, but is likely losers of the war, so that is their punishment, even if is no doubt gonna kill them, and making them stand instead of lying horizantally is bad.
The isekai center was pretty evil, playing with people new lives, and unfair, they know why MC is hated so they could have lowered the lust aura, but the receptionist said it was to see how they behaved, not to help, it was honest.
A isekai reincarnation that works like a monkey paw wish...can't say is not interesting, but outright evil in this case, as if MC had not met the elf he would have been killed or drained.