How can a muslim deny shariah.
It is the core of islam. Islam is not just a religion that tells people to pray. It is a whole code of life. It gives you code of conduct in many daily life situations.
Like for stealing we know the punishment.
For drinking we know the punishment.
For adultery we know the punishment

You take away the punishments, then you are just left with prayers. And then there will no punishment for adultery, stealing etc etc.
The essence of islam is that it tells us if you do something wrong you will be punished. Lets take away the punishment for adultery and suppose we are living in a Western country where adultery is not considered a sin. Do you think there will be anything to stop a person from committing adultery?
There is a huge difference between the West and Islam. If we take away the punishment described in Islam we would be left with a Western society.
NOTE
I dont think the Western system of punishment is wrong. It is just that when we already have our system then why should we be copying others systems