In our extroverted & other oriented culture & society, we have been inculcated w/the premise that 1 is the loneliest(in quite the negative sense) number. We have been further indoctrinated w/the premise that humans are born to be social. Being social is seen as the BE & END ALL to human existence. If one isn't social, it is assumed that something must be wrong w/him/her. That premise & indoctrination is why many introverts are viewed as suspect, off-putting, standoffish, & that word-antisocial. Introverted people & loners are considered to be in need of "fixing" in order to be "more normal" i.e. accepted by our ever-social, extroverted culture & society.
This thinking extends into why only children are oftentimes derided & the common thinking is that a child should have a sibling in order to be social. Only children as w/introverts & loners are viewed as lacking in terms of sociability. Such people are quite comfortable in being alone & in their own company. However, those who are extroverts, sociable, & part of the sibling culture find these things to be weird as they are used to socializing & constantly being w/people. Because of their socialized environment, they can't understand how onlies, introverts, & loners can be contentedly alone, pursuing solitary hobbies & activities. Many extroverts, sociable, & those w/siblings find the pursuits of onlies, introverts, & loners to be quite boring because the latter are at ease being alone while the former are only happy gallivanting about, going from one social activity to another.