SIDE NOTE: To express permission, the word "may" should actually be used. When I was in school, if we asked: "Teacher, can I go to the bathroom?", the teacher might reply "I don't know, can you?" This was a mocking indication that we had used the incorrect grammar to request permission. "Can" references ability or possibility, but is colloquially, and commonly, used to mean permission, even though this is not strictly correct.
Regardless of the word used for the permission, expressed in a dismissive or impatient tone of voice, or at the critical moment in the conversation where its context would be understood as intolerant, saying "You can/may go now" can definitely sound condescending. It can imply that the speaker no longer desires the presence of the one addressed.
English speakers rely quite heavily on body language and tone of voice to interpret meaning--more so than many other languages might. When these non-verbal cues seem ambiguous, misunderstandings are commonplace. In a text-only environment, the reader is left to infer the intent of the speaker based on the context of the exchange, which is prone to mistaken interpretations.
"Social and psychological influences" refer to the affect, or emotional aspect that influences one's thinking based on relationships with others and the suggestions of the mind.
"Condescension" means looking down on someone, indicating the speaker feels superior to the one addressed; "in the right context" refers, not to a "correct" context, but rather to a "specific" or "particular" context or setting.
Suppose you enter a friend's room, and try to talk to him about an idea which you think is great but for which your friend shows no enthusiasm. In fact, your friend rather dislikes the idea--yet you attempt to be persuasive. Clearly annoyed, your friend, to put an end to the discussion, finally says: "You can go now." In this context, you would understand that your friend no longer desires your presence. It is not merely permission to leave, it is a request that you leave. In this sense, "can" can serve as a command.