The part I want to focus on it the text in brackets, where he presents his Makor. He writes
"[See Taz O:C 75:1 who stresses how extremely harmful it is when any part of the upper section of the legs is uncovered.]"Thus, short skirts and mini-skirts are terrible. As it continues from the sources he cites, he the problem is where even less than a tefach of thigh is showing. And read the whole section here.
I have two problems with this.
1) The first is that this seems to me to be somewhat of a mischaracterization of the Taz. The phrasing of the above, and the context in which it is placed, is that the Taz is talking about the spiritual dangers of pritzus. And thus, in warning people about this threat, he stresses the problem of parts of the thigh any part of the upper section of the legs is uncovered. And further, as part of this warning and stressing, he notes that this exposure is extremely harmful.
In fact, the context is explaining some interesting language in the Tur. You can see the Tur here, and you can see the Shulchan Aruch with the commentary of the Taz here.
The Tur is talking about the laws of kriat Shema, such that a man may not read the Shema opposite one tefach of exposed flesh of a woman, where that flesh is usually covered, even if it is his wife. And then he says that if her thigh is exposed, it is forbidden to read Shema opposite the exposed thigh.
This should be the same as the previous bit about a tefach of exposed flesh. So why does Tur go out of his way to mention it? Taz explains that since the exposed thigh causes hirhur, it is forbidden to read Shema opposite it even if less than a tefach is exposed.
Thus, he is not coming to stress the spiritual dangers, and warn us about it. Rather, he is coming up with a diyuk in the language of the Tur. And nowhere does Taz say it is extremely harmful. This is Rabbi Falk's extension of the position that it causes hirhur even with less than a tefach exposed. This may be a valid extension, but it mischaracterizes the tone and message of the Taz.
2) Secondly, this is by no means the only explanation of the Tur. Beis Yosef, author of the Shulchan Aruch, argues. He cites for this the Rashba, based on the Raavad. Beis Yosef maintains that the reason Tur mentions this is that the thigh is only a makom tzanua by a woman (shok beIsha erva), but not on a man. Even though other places on a woman's leg is not erva. Therefore, he is coming to tell us that this is a makom tzanua for the woman, and thus one cannot read Shema opposite an exposed thigh. But the amount of exposure for Shema would be a tefach, just like any other exposed part of the body that is usually covered. And there would be no need to claim a greater spiritual danger. And then the part about the greater harm from "any part of the upper section of the legs," implying less than a tefach, would not hold true.
(That does not mean that it lechatchila may be uncovered. The purpose of these posts, I must stress, is not halacha lemaaseh. Consult your local Orthodox rabbi for guidance.)
Indeed, the Aruch HaShulchan mentions both explanations of the Tur, and says that the latter is more persuasive, and that this was why the thigh was not listed separately in Shulchan Aruch -- it is just like any place usually covered.
Now, Rabbi Falk is free to hold like the Taz over Beis Yosef and others. And it is quite possible that those he follows hold like the Taz. But still, he is giving a one-sided citation here to bolster his message that short skirts are absolutely horrific and extremely harmful. (Others may indeed forbid short skirts, but still hold by Beis Yosef.) This may be a laudatory goal, but I like my quotes in context.
As an interesting aside -- I did not see Rabbi Falk mention this, but then I did not read the entire book. There appears to be a position, cited and discussed by Beis Yosef and Bach, that would permit short skirts and miniskirts for your average Beis Yaakov girl. That would be the position of Rashi. On the shok beIsha erva gemara, which appears on Brachot 24a, we have the set of Rashis pictured to the right.
The first Rashi in the image is discussing an exposed tefach. And he holds that this is specifically if she is a married woman. Just like head hair is only erva for a married woman. And based on the conclusion of the gemara, this is specifically his wife, for reading of Shema.
And the Rashi, dibbur hamatchil "shok" and "erva," he says that this is specifically by a married woman, that it is forbidden to look at a married woman's exposed thigh, and that one cannot read Shema opposite one's own wife's exposed thigh. (Assuming as we have so far that shok means thigh. See also this, for an elaboration of Rashi's position.)
I would venture that most girls wearing miniskirts are unmarried teenagers. Once again, this does not mean that we pasken like Rashi. And perhaps even according to Rashi we could find reasons that one should not wear miniskirts or short skirts. But it still is an interesting position.