Yeah, people get wrapped up in their own emotions over this scenario. There's also the ugly "whaddya want, money?" response which I personally find very offensive. When a newfound relative comes tumbling out of the tree, people sometimes close ranks and go into denial.
"Whaddya want, money?" presumes that the relative is just in it for material gain, a nasty and unfounded belief.
"How DARE you say that my daddy ever loved anyone other than my mama!" I firmly believe the only person any of us ever really know is ourselves, and most people don't even accomplish that. No, you cannot be sure that you know every single thing your parents, uncles and aunts, or other relatives ever did and who they did it with.
"No one in MY family would ever give up a child" again, is breathtakingly presumptuous and naive about the reality of society.
I also suspect that some people power-trip on getting to be the "secret-keeper". You see this a lot in older relatives who might know the identity of someone important or the whens and the hows, but when asked suddenly clam up and act like the world would crack in two and lions would lie down with the lambs if they told.
It's astonishing how someone can wholeheartedly believe they are a direct descendant of Pocahontas' niece Princess Coriander Pussywillow of the Cherokees, based on a Geocities website written in Comic Sans citing no primary sources, but when presented with 1800 shared cMs they become unable to comprehend what's going on and declare that it must be some mistake.