Nice try, attorney representing a town that tried to silence a critic. Unless the law in your state is vastly different from the law everywhere else that I have ever heard of on this topic, slander of title has a specific meaning: doing something that affects title to or an interest in a specific parcel. Negative comments that allegedly diminish the value of all property in a municipality do not constitute slander of title, unless the municipality owns or has a mortgage on all the property within its boundaries. The fact that the municipality taxes all property within its boundaries based on the value of each parcel doesn’t give the municipality an interest in the property.
That’s without even mentioning the obvious violation of the critic’s First Amendment rights.
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