I belive that "no jerks" policy basically means that everybody needs to be nice and civil with each other.
This does not mean that mistakes are allowed and things are done by consensus.
The problem with jerks is that they are jerks: people do not like them and it is hard to work with them and that is not good. Nothing else. Sometimes that is ok - but in many cases it is not ok since team and project needs to grow into other areas where that "brilliant jerk" will not be so brilliant.
The problem is that the meaning of "civility" is mutable. Too often, "being civil" or "being nice" or "being respectful" ends up meaning going along with the flow and not challenging the group consensus.
This does not mean that mistakes are allowed and things are done by consensus.
The problem with jerks is that they are jerks: people do not like them and it is hard to work with them and that is not good. Nothing else. Sometimes that is ok - but in many cases it is not ok since team and project needs to grow into other areas where that "brilliant jerk" will not be so brilliant.