Food habits: Swami Vivekananda was a Non- Vegetarian. Yes! he was. In Sanskrit they have told, jeevo jeevasya jeevana.( If one life has to live then, it has to eat another life). He strongly believed that "The Integrity of the men cannot be judged by his profession, but by his conduct, food is for the body, and conduct is for the soul." You can eat meat and still be a good person and a devotee of the god. He said that if India wants not to be vulnerable then Indian people at large must start consuming non-veg food, as non-veg food is essential for you to be fit for adverse conditions. In his own words..
About vegetarian diet I have to say this - first, my Master was a vegetarian; but if he was given meat offered to the Goddess, he used to hold it up to his head. The taking of life is undoubtedly sinful; but so long as vegetable food is not made suitable to the human system through progress in chemistry, there is no other alternative but meat-eating. So long as man shall have to live a Rajasika (active) life under circumstances like the present, there is no other way except through meat-eating. It is true that the Emperor Asoka saved the lives of millions of animals, by the threat of the sword; but is not the slavery of a thousand years more dreadful than that? Taking the life of a few goats as against the inability to protect the honour of one’s own wife and daughter, and to save the morsels for one’s children from robbing hands - which of these is more sinful? Rather let those belonging to the upper ten, who do not earn their livelihood by manual labour, not take meat; but the forcing of vegetarianism upon those who have to earn their bread by labouring day and night is one of the causes of the loss of our national freedom. Japan is an example of what good and nourishing food can do.
(Complete Works, 4.486-7)
Religious Conflict with his opinions: Moreover Swami Vivekananda has compromising attitude. He tried to compromise with evolution theory as he didn't want his religious belief to be conflicted with science. That was contradicting many of his followers beliefs.
The communists used him for his followers vote bank.. Communists called him as "revolutionary" just like Cuba's Castro called Jesus as revolutionary. Many Hindu gurus of his time felt that a beef eating person can't be the face of Hinduism when he's delivering speeches in foreign countries.
Hate Speech: When Swami Vivekananda visited Kerala, he went to a temple in Shornur located in Palakkad district. The devotees asked him that his whereabouts, caste but instead he started to speak about why we should not consider castes system. The nair devotees were not in a mood to hear him so they caught his neck and kicked him out. This was a big shock to him. It is said that this is why he did not intend a public speech in Kerala. He got angry and he abused mallus(Kerala people) in speeches in other states .He even called kerala as mad peoples house.
But in other parts of India, he was welcomed and he delivered speeches.
Nonetheless he was a key figure in the introduction of the Indian philosophies of Vedanta and Yoga to the Western world and is credited with raising interfaith awareness, bringing Hinduism to the status of a major world religion during the late 19th century. He was a major force in the revival of Hinduism in India, and contributed to the concept of nationalism in colonial India. Swami Vivekananda is regarded as a patriotic saint and his birthday is celebrated as National Youth Day in India.