That is an honest and genuine concern if people were trying to promote standards of modesty without proving they were a thing in the first place, but it is provable.
Here:
Sacra Propediem (Pope Benedict XV)
http://www.vatican.va/content/bened...s/hf_ben-xv_enc_06011921_sacra-propediem.html
Comentarium Pro Religiosis (vol. 9, 1928, pp. 414-415) includes the call for a crusade against immodest fashions by Pope Pius XI
Bishop Douville of Quebec in a pastoral letter quotes the modesty standards set by the Pope’s Cardinal Vicar.
Phillipine Bishops accepted this Roman standard for modesty and issued it in their Dioceses.
On December 6, 1959 His Eminence Rufino Cardinal Santos, Archbishop of Manila wrote a pastoral letter approving of the Phillipine Bishops’ work in doing this and he listed the standards set by the Pope in his letter.
Father Bernard A. Kunkel, with ecclesiastical approval, made a modesty crusade and got the apostolic blessing of Pope Pius XII. All who further the work of the modesty crusade are given the apostolic blessing also.
If all these people quote the modesty standards from the Vicar of the Pope, and these people are literally Bishops and other clergy, then why would it be false?
Padre Pio also held these standards and would refuse to hear confession from a woman wearing immodest clothing.
Pope Pius XII Address to the Latin Union of High Fashion on November 8, 1957:
“The most insidious of sophisms, which are usually repeated to justify immodesty, seems to be the same everywhere. One of these resurrects the ancient saying ‘let there be no argument about things we are accustomed to’, in order to brand as old fashioned the rebellion of honest people against fashions which are too bold …” This fallacy consists in the implied notion that sin stops being sin as soon as one gets used to it. Imagine how many kinds of sin could be whitewashed in this way! The fact is that man can, so to speak, ‘get used to’ just about any sinful practice that might be mentioned—promiscuity, fraud, cheating, lying, etc.—but that does not make it any less offensive to God or less deservIng of divine punishment. It" is a common thing for such a one to say. though actually in self-condemnation, “It doesn’t bother me at all… I see nothing wrong in it…”
He also says in this address:
“There always exists an absolute norm to be preserved, no matter how broad and changeable the relative morals of styles may be … Style may never give a proximate occasion of sin, and clothing must be a shield against disordered sensuality.”