It would be difficult to prove what the person spreading the falsehoods knew or believed. For example, Donald Trump lied with nearly every utterance, but many of the lies he told were out of ignorance. He is a bullshitter. Someone who bullshits makes statements without regard to the truth. Sometimes a bullshitter tells the truth, and sometimes they lie. They don't care whether the statement is true or false. They make statements to forward some goal of theirs. A callous disregard to the truth may be undesirable, but it would be very difficult to enforce a ban on it, or a ban on falsehoods generally. It's just too difficult to prove what someone knew or did not know without a direct admission of guilt. Unless someone specifically admits to telling a lie, and doesn't recant by saying they were mistaken, how could you prove what they knew? Would you prosecute someone who makes false statements out of ignorance? We would all go to jail for that one.

Unfortunately, the only defense against falsehoods or ignorance is to learn the facts. The real problem is to decipher why someone wants to believe lies. If you examine most public statements out of Senator Ron Johnson, you see a pattern of false statements that specifically pander to right-wing desires. He makes statements he knows are not true but that the people who support him want to believe. Who is to blame for that? Ron Johnson, a political opportunist, or the people that eagerly consume lies because they like the taste?