"There is nothing either good or bad but thinking makes it so." This Shakespeare's saying is largely true. Thinking depends on many factors, a person's genes, his upbringing, environment, parental guidance, teachers but most importantly of all, his community and the religion to which he belongs.
Take the case of food. One man's food is another man's poison. For example, most of the Hindus are vegetarian and partaking of meat is poison to them but for Hindus and Sikhs like me, there is nothing wrong in taking meat although Sikhs and some Hindus insist that it should be jhatka where the animal is killed with one stroke.
Moreover, generally Hindus do not eat beef. Christians and Muslims find it nothing wrong in taking meat but Muslims do not consume pork at all and insists that the meat (primarily chicken and mutton) they consume should be halal meat i.e., before killing the animal, the verse, "La ilaha ill Allah, Muhammad ur Rasul Allah" is recited so that the animal becomes immortal.
Now, take the case of marriage. Hindus particularly in Haryana feel that one should not marry in the same gotra and if somebody defies it then he alongwith his spouse is likely to be put to death. Sikhs generally feel that one should not marry in his gotra but some Hindus and Sikhs do marry their cousins but of different gotras.
Although in our family, marriage with cousins is not allowed yet my father's younger brother's son married his cousin who was the daughter of his mother's brother because both the boy's parents and girl's parents were agreeable to it. Christians and Muslims find it nothing wrong in marrying their cousins even of the same gotra (clan).
Lets consider politics now. It is alright for a Hindu or Sikh or Christian who is Indian to think that we should have a defence alliance with Israel to counter Sino-Pak axis but for an Indian Muslim, it is extremely difficult to think like that.
Indian Muslims feel that a State for Palestine should be created and Israel should withdraw from the West Bank but Indians other than Muslims have no definite views in the matter except a few leftists.
Indian Muslims feel that there should be a quick settlement of the Kashmir issue and they generally regard it as a dispute, but Hindus and most of the Sikhs feel otherwise and consider the entire J and K to be part of India.
So, to conclude, I think that Shakespeare was right in observing that nothing is good or bad; only thinking makes it so.