The first is probably tough to prove. Certainly one could argue that there was cultural an political credibility at stake, something very prized by imperial powers. However, I feel that any such 'vested interest' could be known only to a few, and hence not be significant enough to direcly influence procedings.
The second point is without doubt the case, as can be seen by the reaction to almost all forms of social change at or around that time. The third option would be difficult to substantiate, but I have no doubt that flat earth societies would have been perceived as radical, and hence a threat- remember, this is a time when belief in social 'normativity' is a truly all-conquering force.