If one's moral framework is not explicitly based on Judeo-Christian doctrine (regardless of its actual ontology), there would be no reason to include Jesus or any other component of that doctrine when teaching it.

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Lack of visitations from the future (so far as we know...) would reinforce the assertion that time travel to the past is impossible, but it wouldn't conclusively prove that this is the case. It might still remain possible, but not something that has actually occurred. Alternatively, such a visitation might have occurred but was not detected. Or the act of "backtiming" creates a dimensional fork (as in multiverse theory), and we are in an undisturbed stream. Or several other possibilities, none of which can be incontrovertibly ruled out given our current understanding of spacetime.

But fwiw, my bet is on backtiming being impossible...