I looked up more about that concept and also found that supposedly "Prop 8 = Less Government". I don't see how free speech has anything to do with it.
The proposed amendment is quite short:
SECTION 1. Title
This measure shall be known and may be cited as the "California Marriage Protection Act."
SECTION 2. Article I. Section 7.5 is added to the California Constitution to read:
Sec. 7.5. Only marriage between a man and a woman is valid or recognized in California.
Free speech is not in there, but it will add government restrictions to marriage. That's more government, not less.
The concern about free speech is apparently because church leaders and teachers won't be able to continue to preach against same-sex marriages if they are legitimate.

After I wrote the above, I went for a walk and saw this house down the street.