Liberals are not proud of America, because they are perpetually angry about things they perceive as being wrong with America.
They constantly complain about how unfair capitalism is, how we have original sins such as slavery, which have never been atoned for, etc.
They complain that we are despoiling the environment, even though the air and water are far cleaner than 50 years ago.
They complain that conservatives are racist, sexist, etc. as per Hillary’s screed.
They think every grievance group, from racial minorities to homosexuals, are somehow being oppressed, in spite of major changes in rights for such people in recent decades.
Their whole thought process is negative, in my opinion. They only talk about perceived wrongs about America, without any consideration given to what is right with America.
In fact, those grievance groups are engaged in oppression. If we White Men were the monsters the grievance groups accuse us of being, the grievance groups would not exist.