havent read the manga properly and now i have questions?

Hydroalbidius said:
you know when a story deviates too much from mc to focus on side characters to give info dumps I don't like it as it is annoying.

so here are few of my dumb questions

1. why did mephisto has created the exorcist organisation?

2. why they are trying to bring satan into human world if they knew that things will get out of control?

3. if exorcist feel so repulsive about demons because demons harms humans how would they feel about these demons possessing a human body

4. and do people agrees to let their body being possessed, I guess they are unjustfully being put through these experiments. and how did shiro fujimoto don't want to kill these mf who killed his siblings

the series somehow makes the good guys look evil to me