What's With The Anti-Sharia Law Marches ???

According to this report, there have been nationwide marches against Sharia law:

http://www.nbcnews.com/news/us-news/anti-muslim-act-america-stage-marches-against-sharia-law-nationwide-n767386

I do not support Sharia law in any way.

But I do have a question: what does this part of the US Constitution mean?

Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof

If Sharia law is part of the "free exercise" of Islam, then why is it not permitted in the US?

Here is a better discussion of the issue:

Sharia will never become 'the law of the land', neither will Halakha or Catholic Religious dogma, but for observant Catholics, Muslims and Jews their institutions are an important part of religious practice. Providing that state and federal laws are observed, and participation is voluntary, their function is one of mediation, community cohesion, and of course the enforcement of religious rules on people who choose to be part of their community.

You can read the rest @
http://www.danielpipes.org/comments/180931

I completely agree that Sharia law should NEVER be forced upon Americans, but do we have a right to stop its voluntary implementation by Muslims who desire it in their own communities?

I have a feeling that before this issue is fully decided, there won't be ANY religious tolerance left in the US.