There is a huge difference between theory and practice. Though Guru Nanak's Sikhism teaches to abandon caste-ism, rituals, etc., etc. but in practice this is not followed. Casteism is very much prevalent in the land of the Sikhs that is in the Indian Punjab as well as in the Punjabi Sikh diaspora. Even the Gurdwaras are not spared, they too are caste based. You might have noticed, Punjabi Sikhs proudly displaying the board outside Gurdwars that says Ramgarhia Gurdwara, similarly some Gurdwaras are built and are meant for the Jat Sikhs. Punjabi Sikhs will often preach that we are One, we are Sikhs, we don't follow Casteism but indeed they are divided into Arora, Khatri, Jat, Ramgarhia, etc. irrespective of them living in Punjab or even those of the Punjabi origin living abroad.