There are a number of...

There are a number of European countries which prosecute such things as holocaust denial. These limits on free speech are based on the experiences of these countries during WWII, whether allied with Germany or occupied by German forces. But it remains unclear whether prohibiting these views has a good or a bad result. Our constitutional system is different. The British Parliament for example can pass many laws about many things which our Congress is prohibited from doing: such as, to take an absurd case, to forbid people with natural red hair from entering politics. Parliament has no real limits on its powers.
Perhaps the best answer is for people in power of good will with the "right views" to take initiative against dangerous and hateful ideas and policies. Unfortunately such people are not always easy to find, certainly not now when the Grand Old Party has become entirely the Trump Old Party or the Greedy Old Party.