Re:Zero kara Hajimeru Isekai Seikatsu

[KrayZ33]

They take him out of the equation, without knowing what the equation was?

What's so hard to understand about that.

If I play against 1 player instead of 2, it's obviously easier to plan around.

Assuming he was an evil cultist (which they don't even know), what if he already set a trap? What if he had allies incoming? What if he is mind controlling Ram and Emilia with some strange power? They basically know nothing and decided to not find out anything more.

They spoke to him for a few sentences and judged him based on that. The moment they felt he was a danger, they should've tried to find out more. At the very least, they should've interrogated him when he was imprisoned. It would not be ideal, but I would at least understand that.

So what if they had asked him, what would have changed?
It all comes down to Garf not believing him anymore.

Him attacking Subaru the first time they met does have a reason, obviously.
Experience, most likely.
I feel like we are blaming the guard dog for guarding the house.