Complex sentence: Many suspiciously motivated practices are not comprehensively covered by the rules of chess and so, on ethical or'moral conduct' grounds only, may be judged by some as acceptable, and by others as cheating.
Split into simpler sentences: Many suspiciously motivated practices are not comprehensively covered by the rules of chess. On ethical or moral grounds only, such practices may be judged by some as acceptable, and by others as cheating.