Allah has strictly forbidden in Qur’an to announce acts as haram or halal from one's own desires. Making something sacred that God has not made so. This act rises upto the level of shirk. Even trivial acts like slitting the ears of the cattles in the name of God was severely rejected by God.

Why would God not like it? Is God a jealous god? Do His feelings get hurt if someone makes something sacred which He did not declare so? Is there some kind of personal 'Divine problem'? Naoozubillah. No not at all!
The problem is that by making something sacred which God did not make so, you can obscure the Truth.You can be a reason to create a barrier between that person and Truth to whom you are trying to prove that something is sacred-which actually is not.

Take the example of declaring the prophet Uzair (pbuh)the son of god by the Jews. When initially this was introduced, there was no intention of making or calling him Son of God in the literal meaning. It was to portray him as His spiritual son considering his highness and piety and closeness to God.
However what happened as a result of this self introductory sacredness which apparently looked very innocent and harmless? When Christians called Jesus/essa(pbuh)the son of god, they took it in literal meaning! They declared him one of the three in Trinity. Many religious people left this belief and became atheist because of this added concept to Christianity as they could not relate this fact to logic. How can god be a son of god and then be borne of a woman, in blood and slime? Then the mother of this god should be a bigger god--- and so on...confusions went on.

Hence we can imagine the disastrous effects of pronouncing things sacred which have not been done so by god or his final prophet Muhammad (pbuh)

Complete segregation of women in Islam is one example of such. Reasonable research into Islamic history has proved that men and women prayed in the same masjid in Medina at the time of the prophet sws and interacted with eachother. There existed a friendly & family environment in the mosques. But we can see in Muslim world today how this concept of total segregation of the two genders has crept in.

I was surprised to know the other day that a religious conference in a hotel in UK was postponed because the hotel management had failed to put up a screen between the men's and women's section. The in charge of the women's group sent the message to the hotel management that if they did not have a screen they better get the bed sheets off the hotel bedrooms and make a screen between the men’s and women’s sections! Although the seating arrangement was in two sections already.

Can we imagine ho many people today in the West, Muslims and Non Muslims equally, have been moving away from Islam because of this self implicated rules of making the acts sacred which were never done by Allah and Muhammad sws???

Original idea adapted from: Dr.Jeffrey Lang's Lectures.
http://onlineislamicstore.com/a3850.html