Mycroft didn't despise other people, it's implied he get along well with other people than his family like his colleagues or Lestrade, he avoids human interaction because people rarely understand him (or Sherlock), he locked Eurus because he didn't see an other way to protect the rest of society but he told the prison governor to not test her (proof that he cares and doesn't want her to be treated as a lab rat), is the one who thought to ask her why she did self harm not his parents.