2. Abodah Zara 26b is taken seriously out of context. What the original says is "but minim [idolatrous priests, whether Jewish or gentile], informers, and apostates [specifically Jewish] may be cast in [a pit], and need not be brought up." This says nothing about killing, and much less about killing gentiles. If it says anything about killing, Jews are included. The discussion, however, is whether a gentile may circumcise a Jew. The argument about who may be thrown into a put, pulled out but not thrown in, etc., concludes by saying that the pit should be covered so that nobody goes in.
I'm glad you cleared that up. But is the pit covered before or after the minim is thrown in? And are we talking a deep pit or a little indentation in the ground? You would think a book of law would be more specific on these matters.