Some people say that even when alternative medicine is proven wrong, we should not do anything against it. "If it doesn't work and it does no harm.
Why don't we let people keep going to alternative practioners if they want to do that?" The problem is that usually there is harm.
Some general arguments that apply to all disproven or unproven (and therefore to be regarded as wrong until proven otherwise) alternative medicine is
that people will not seek convential treatment. This can worsen the disease. However, there are also cases where a pseudoscientific alternative
treatment does the harm itself. Attachment therapy is one of those.
The article
The Etiology of a Social Epidemic gives a good synopsis of
attachement therapy and its problems:

The last decade has seen a sharp rise in the number of cases of gross child abuse, some resulting in death, by or under the direction of
"psychotherapists"--many unlicensed or delicensed, who practice a form of pseudotherapy called Attachment Therapy (AT).
AT is a growing, multi-faceted and as yet underground movement for the treatment of children who pose disciplinary problems to their parents or
caregivers, in many cases adoptees or foster children. These children are diagnosed as suffering from Reactive Attachment Disorder (RAD), a failure to
attach with the current caregiver due to early trauma.
The only cure (according to AT) is to "reparent" the child, thereby supposedly obtaining the desired attachment and total obedience of the child.
Reparenting methods include eye contact on command, physical restraint, the infliction of pain and terror, and the induction of regression.

There is no scientific evidence that attachment therapy works. There are conventional therapies that do work, but they take much longer than the time
it takes attachment therapy to work, if we are to believe the proponents of attachment theory. The article
Quackwatch: Be wary of attachment therapy ends with the following conclusion:

Dr. David Waller of the University of Texas Southwestern Medical School says of restraint model therapies, "My personal opinion of these
so-called therapies is that they are very controlling, manipulative, aggressive, abusive ways of adults behaving toward children, in the guise of
treatment." (Waller, 2001) There are many effective treatments for Reactive Attachment Disorder. (James, 1989) Claims of quick cures and anyone
promising a "different" child in two weeks are preposterous. Parents and professionals who to claim that traditional therapies do not work on
Reactive Attachment Disorder must be reminded that their statement is not supported by scientific evidence and that there is no excuse for torturing a
child in the name of therapy.

Abuse and torture are the words to use for attachment therapy. There has even been a case of a death caused by attachment therapy: the death of
Candace Newmaker,
Scientific American: Death by
Theory:

Candace was treated by Connell Watkins, a nationally prominent attachment therapist and past clinical director for the Attachment Center at
Evergreen (ACE) in Colorado, and her associate Julie Ponder. The treatment was carried out in Watkins's home and videotaped. According to trial
transcripts, Watkins and Ponder conducted more than four days of "holding therapies." On one day they grabbed or covered Candace's face 138 times,
shook or bounced her head 392 times and shouted into her face 133 times. When these actions failed to break her, they put the 68-pound Candace inside
a flannel sheet and covered her with sofa pillows, while several adults (with a combined weight of nearly 700 pounds) lay on top of her so that she
could be "reborn." Ponder is reported to have told the girl to imagine that she was "a teeny little baby" in the womb, commanding her to "come
out head first." In response, Candace screamed, "I can't breathe, I can't do it! ... Somebody's on top of me.... I want to die now! Please!
Air!"

Until they prove that attachment therapy does work, it should be forbidden. In this case the decision is easy. But there are also other kinds of
alternative therapy. I have a simple opinion: we should only allow treatments are scientifically proven to work. Is this too much to ask? If
attachment therapy, homeopathy or any other kind of alternative medicine work, they will easily be proven to work and they will be used. If they are
wrong, they will not be used and we keep our health system free of useless non-working treatments.
More about attachment therapy:
Advocates for Children in Therapy.