(also known as: Constitutional rights fallacy)
Description: When one gives a reason for one's rights (constitutional or other) with what one should do. This is common among staunch defenders of "rights" who fail to see that rights are not the same as optimal courses of action. It can be a way of attempting to hide the fact that the "should" is based on one's subjective moral values (or at least values that are not shared by the opponent) rather than a more objective law to which virtually everyone acknowledges.
Person A should not have done X.
Person A had every right to do X; therefore, person A should have done X.
Carl: Hi Billy, it is great to meet you! I think you will be happy here at Friendly Manufacturing, Inc.
Billy: Hey, you're Irish! Irish people make great factory workers—that is where they are happiest. I am surprised to see you in management.
Carl: Excuse me??
Billy: Don't mind me. I am just expressing my Constitutional right to freedom of speech. Do you have a problem with our Constitution? Do you hate America?
Explanation: Billy is clearly ignorant when it comes to the realities of cultural differences, and he seriously lacks social skills. He is correct that he has every right to express his opinions, but he does not seem to mind offending and hurting others by making his opinions known. Constitutional rights do not exist in a vacuum—they are part of the larger system that includes social conventions such as tact, appropriate behavior, and kindness.
A top reality TV superstar from the hit show "Goose Galaxy" recently did an interview with GM magazine (Geese Monthly). In this interview, he told the interviewer that, according to his beliefs, the galactic emperor has decreed that all MAC users are "sinful" and MAC use leads to having sex with computers. When many MAC users and non-MAC users alike expressed their outrage at what they felt was an offensive and demonstrably false proposition, defenders of "Goose Galaxy" screamed that the TV superstar had every right to say those things as his speech is protected by the First Amendment.
Explanation: The claim made was that the comments were offensive and demonstrably false (as no research has been able to demonstrate that MAC use leads to having sex with computers), and the reality TV star should not have said those things, yet the "Goose Galaxy" supporters countered with the fact that the reality TV star had the right to say those things; therefore, he should have. Notice that no claim was made about rights—this is a strawman. The fallacy extends beyond the strawman because the defenders of "Goose Galaxy" are conflating the reality TV star's Constitutional rights with the claim that he should have said those things.
Exception: When one's values are in line with the rights, then claiming one "should" exercise his or her rights is not fallacious—as long as the reason given does not have to do with rights:
I feel that it is morally wrong to use a MAC; therefore, I should speak out against MAC users; and yes, it is my Constitutional right to do so.