I'm going to do my best to wrap up
my end of this incredibly long discussion
I suppose what my underlying point is, is that I hesitate to adopt a
qualitative means to determine what is human. This is because of everything you brought up; the mutations, the defects, the diseases etc. all make some people considerably different from "regular" people. I prefer using DNA, a more quantitative device, because it leaves no room for shades of gray. A quick analysis of someone's genetic material and you immediately know if it's human or not. The questions you ask are excellent ones, namely "where do we draw the line?". It is a question that is unanswerable unless you make up an arbitrary set of regulations (i.e. "to be human, the being must have no more and no less than two legs", a statement that would rule out the Indian girl in your picture),
OR if you have something that is both common to all humans and that is easily analyzed. DNA seems to fit this perfectly, and therefore we can avoid making shady rules as to what is human or not.
As you said, human DNA is also very similar to monkey (or ape... or maybe both; either way...) DNA. You bring up a valid concern that it is similar enough that they too could be classified as "human" by DNA. Unfortunately, I am no geneticist, so I simply don't know by what exact amount monkey DNA is different from human DNA. However I
do know that forensics instigators have never accidentally incriminated a monkey for a crime because they couldn't tell the difference between monkey and human DNA. Obviously, they are different enough that the distinction can be made. Also, in the case of mutations and the like, I don't think they cause such a radical change in the DNA that the DNA becomes completely undefined as to its species, but again, I am no geneticist.