Why sense gratification is considered bad?
“People in this world want to satisfy their senses, they have become mad, and in this madness, they’ll do anything and everything. For example, there have been many instances in material life where someone has become mad after something and has committed a criminal act such as murder. The person could not check himself. Similarly, we are accustomed to sense gratification. We are mad, and therefore our minds are fully absorbed in karma. This is very unfortunate because our body, although temporary, is the reservoir of all misfortunes and miseries; it is always giving us trouble. These matters are to be studied. We should not be mad. Human life is not meant for that. The defect of the present civilization is that people are mad after sense gratification. That is all. They do not know the real value of life, and therefore they are neglecting the most valuable form of life, this human form.”
Source: A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “The Science of Self-Realization”, Page 161