Because the difference between treating someone ‘humanely’, and treating someone as though they were Christ (or, anyway, as though they were our brother or sister in Christ, as the saying goes), is that the definition of that word, ‘humanely’, can change according to what the person doing the ‘treating’ thinks the definition ought to be, whereas Christ does not change, and will always call us to a certain action, or orientation, even if not everyone will interpret this call correctly (meaning, some will get it right and some will get it wrong).