What the hell gives them the right to do this?
Why, the bible, of course. Although it's not jesus, but paul, the first catholic, whose words are applied.
Below is the wt quote. I italiced and yellowed the scripture from paul.
*** w81 9/1 pp. 20-21 Happy Are Those Whom God Corrects ***
Continuing in the counsel to the Thessalonians about the lazy, disorderly ones, Paul wrote: "If anyone is not obedient to our word through this letter, keep this one marked, stop associating with him, that he may become ashamed. And yet do not be considering him as an enemy, but continue admonishing him as a brother
." (2 Thess. 3:14, 15) Hence, Christians can ‘mark’ someone who persists in disregarding God’s principles.
We need, however, to exercise great care in applying this divine counsel. In our imperfection, we might tend to make personal judgments based on individual likes or dislikes, such as about styles of dress or grooming. But if a sister’s clothing, for example, is not immodest, indecent, or shocking to the brothers in general, we should recognize that she simply has a different taste or preference. (Gen. 37:3, 4; John 19:23; 1 Tim. 2:9, 10) We have not been made judges of our brothers and sisters on inconsequential matters of opinion, taste or variations of conscience. (Rom. 14:4, 10-12) Or, even if someone is incorrect on what is really a minor point, we must recall Jesus’ advice:
"Stop judging that you may not be judged; for with what judgment you are judging, you will be judged; . . . Why, then, do you look at the straw in your brother’s eye, but do not consider the rafter in your own eye?"—Matt. 7:1-3.
However, what if there is someone who is significantly deviating from God’s principles, perhaps being grossly lazy or critical, a ‘profitless talker’ who is a constant ‘meddler with what does not concern him’? (2 Thess. 3:11) Or, the problem may be one of scheming to take material advantage of others, indulging in entertainment that clearly is improper, or getting involved in questionable conduct that does not at this point merit judicial action. The elders have tried to help him, but he persists and may be affecting others in the congregation or presenting a danger to others. The elders can discuss the matter and may assign one of their number to give a firm, direct Scriptural talk on the matter to the congregation. Without mentioning the "disorderly" one by name, the elders may thus be able ‘to shut the mouth of’ such an unruly one.—Titus 1:10-13.
Should such a situation exist in a congregation, individual Christians might feel obliged to ‘mark’ the person. Paul explains what this, in part, involves, saying: "Stop associating with him, that he may become ashamed." (2 Thess. 3:14) That would mean your curtailing social involvement with the "marked" person. You should not announce or publicize your private decision, nor try to influence others. But you personally would avoid the company of the "marked" person, in keeping with the healthful counsel given by the congregation’s elders. You would not, though, reject him altogether, for he is still your brother, a fellow Christian for whom Christ died. Rather than allowing any seeds of "hate" to develop, you should "reprove" him. How? Well, in addition to being a good example yourself, your kindly but firmly obeying the direction "Stop associating with him" is one form of correction. But you can do more to help.—Lev. 19:17; Titus 2:7, 8.
You will still be around the "marked" Christian at congregational meetings and in the field service. Thus, you may have occasion to carry out your other obligation involved in ‘marking’ him: "Do not be considering him as an enemy, but continue admonishing him as a brother."
(2 Thess. 3:14, 15) If you did not fulfill your responsibility as to this aspect of God’s counsel, but treated the "marked" person as an enemy, your course might be as unloving as his.
It is to be hoped that the "marked" individual will become ashamed. He may realize that it is by Scriptural direction that you are avoiding his social company. This discipline may help him to "straighten up the hands that hang down and the enfeebled knees, . . . that what is lame may not be put out of joint, but rather that it may be healed." In view of the vast numbers of loyal brothers associating with God’s congregation today, likely it will be seldom that Christians are obliged to ‘mark’ a disorderly brother. But when this does occur, perhaps correction, combined with continued admonishing, will ‘yield peaceable fruit, namely, righteousness.’—Heb. 12:11-13.