This is obviously wrong. Lying is broadly protected by free speech but firmly illegal, not just inadmissible, in court testimony. Courts also have the ability to compel testimony under criminal penalty, while free speech includes the right to say nothing or dissemble. Evidentiary standards place further requirements even on the source of what you are saying, regardless of its truth.

Or as the 6th Circuit put it, "The courtroom is a nonpublic forum, where the First Amendment rights of everyone (attorneys included) are at their constitutional nadir."