Fasting and washing are not part of the LAWS of sharia. Making sharia law illegal needs to be done to send them a messgae.
Actually, they are. Sharia law has seven major areas:
With every piece of the law, comes a punishment. For example, in Sharia, a woman must remain covered- in our society a woman can freely choose it. In Sharia, however, comes a punishment for this if she doesn't, idreb or beating. The punishment aspect is what is already illegal in our society and not compatible. Thus, it is already illegal to practice full Sharia law in this country, it isn't however, illegal to freely choose to follow many of the practices of said law as long as you don't cross the line into violating another's right.
If you have a blanket law making Sharia law illegal, you are also making illegal private practices within it that don't violate other's rights.