I don't think people were upset with the idea of their dream experience being theirs necessarily, but what should be disturbing is the lack of manners in the want to simply invade somebody else's dreams. Invade, as a word, cannot be separated from its negative connotations because it implies in its meaning the specific intent to commit malevolent actions on another human being or a group of human beings by means of intrusion. Assuming shared dreaming is real for the sake of argument, as a matter of etiquette, of pure common human decency one should, upon making a connection with another dreamer immediately present themselves to said dreamer and ask their permission to take part in their experience. To do otherwise is not only extremely rude, but suggests negative intentions. If you mean no harm, why would you disagree with the idea of immediately introducing yourself and asking permission to share an experience?