the rights most worth defending
The rights most worth defending are those that are so unpopular with the majority that insisting on exercising them is likely to cause their removal. Protecting the right to the most appalling expression makes for the difference between freedom for all and selfish regard for the like-minded. Granted that unpopular exercise of a Constitutional right is likely to cause its revocation, the likelihoods of repression are as may be, but taking them as grounds for self-censorship is undignified.