I don't mind stealth robots.  In fact, when I write my second character it will be an android (sexbot) designed to act and appear human.  I just have a problem with it being completely indistinguishable from humans for four reasons:
1) I guess it's semantics, but if it's indistinguishable from humans, in what way is it not human?  
2) It has superhuman strength and reflexes, not to mention blades in its forearms, so not really indistinguishable, just well disguised.  Maybe it has devices to confuse sensors and make it look human on scans?
3) How does it know it isn't human if it can't tell the difference?
4) It's kind of OP.

A cyborg would be cool, though.