As long as no one attempts to use the coercive powers of govm't to spread and promote it, they can exercise it all they want.
But people are using the coercive powers of the government to prevent the free exercise thereof.
Witness the ACLU using the power of the judiciary to force on an unwilling constituency the wishes of the minority who, since they can't get their way by any other means, bring lawsuits to force public schools to do THEIR bidding. It doesn't appear to matter to some that the majority of taxpayers who are supporting the schools with their coerced taxes to educate their own children, object to it, and are forced to acquiesce to the demands of the few.
That's not OK either.
What about using the coercive powers of government to snuff it out? Is that the same thing?