Are you saying that sleeveless shirts are a gateway to p@rn? And just so that we are talking about the same thing- this is what I am talking about, not some immodest undershirt.

In itself it may or may not be a gateway. That is beside my point. My point is it is part of the miasma of our rotten sexual culture, and that miasma is the gateway, and anything (reasonable) we can do to break apart that miasma is good. (Especially when there have been so many authoritative teachings on it. It isn't like individual Catholics made this stuff up.) Inasmuch as this sounds extraordinary would maybe show us how much our Catholic sense does not grasp well modernity. As for the picture, let me just clue you in to the lustful male mind. Some of you men will admit this if you are honest.
First the only thing that is problematic is the sleeves. They reveal too much. By the way, I am not excusing people who have a truly disordered and evil mind, who would lust after a woman in a burqa, I guess. But it is not disordered (apart from sin), to find the female body sexually arousing. It is our nature. And if it is disordered for a man to lust based on the bare arm of a woman, then, given the moral directives of the Popes and the tradition of the Church, it is disordered to expose that bare arm and expose your fellow man to an occasion of sin. Think it through (and read up on scandal:
http://www.newadvent.org/cathen/13506d.htm, and complicity in sin,
http://www.newadvent.org/cathen/01100a.htm). After reading, even if such dressing wasn't scandalous strictly speaking, it would still be an offense against charity since it is virtually impossible to not behold a woman in ordinary society.
So if I am right, you should follow the precepts:
"To prevent scandalizing another we must never transgress the negative precepts of the natural law, nor its positive precepts in cases where they truly bind"
And if you are right, and such precepts are "extreme", you should still follow the precepts:
"It is not permitted to pass over any precept whatever in order to prevent pharisaical scandal, but we may and even should, in special cases and for one or two occasions, pass over a precept whether Divine or human, to avoid scandalizing the weak."
Now some ways that men could lust based on immodest dress. These are all options on board for a lustful man. (I won't take the obvious example we probably agree on: super short skirts, bare midriffs, etc) For the mature crowd here:
- low cut top : look at cleavage (which also draws the eye to the breast), look down women's shirts, sometimes see the bra edging when it is lace, the color of the bra
- sleeveless : most men find the upper arm tender/soft (much more so than the forearm), look the arm pit, you can look into the arm hole to look at bra, maybe see the side of her breast
- backless : also men find the back of a woman to be tender. also if we see that there isn't bra strap, then we going imagine about her not wearing a bra, and we will then try to view her front to determine this (again, just for lustful pleasure, but it was sparked by a backless dress)
- short skirt : the back of the knee some men find tender, if we going to the thigh then there is a lot of trouble coming, when women sit, we try to look up their skirts -- shorter the easier, sometimes a short skirt rides up and you see her thighs, you try to look at her underwear
- tight fitting : look at the figure of a woman, each man likes a different kind of figure, but when it is unduly revealed, it is an occasion of sin, we also try to look at nipples protruding, sometimes the outline of a bra and underwear will be enticing (especially if it is a cut which is meant to entice), tight fitting clothing also helps lustful men imagine the sexual act more clearly, i.e., how would it be to hold her in my arms, open her legs .... (you get the point). Tight clothing leaves little to the active imagination. Bathing suits are also a big problem here. It is not very hard to clearly get a sense of a woman's nipples and areola and vagina area (also maybe some pubic hair) when she is in a tight bathing suit, especially when wet.
- transparent frabric : the problem with semi-transparent is it leaves enough mystery that them is more activity to imagine what the full deal is, transparent fabric are a no-brainer to me, but the most common would probably be thing that reveal the arm, or back, and also in certain circumstances, the chest. These fabrics also enhance the "tenderness" of a woman in a way that is very sexually attractive.
I can go on and on. You get the point. This is all based on normal male sexual desire. We are cued to react to sexual stimuli. If the Marylike standards were employed, very very few of these stimuli come up. In my own case, when a woman is modestly dressed, I immediately have respect for her, and generally note mentally beauty without reference to sexuality. Once the modesty starts to be compromised, that is when sexuality begins to be referenced (lust). If other men aren't willing to admit that they are challenged by these or similar things, (and that is most men, since most men sin through the eyes), then I commend you on overcoming this. Don't kill the discussion for others who do, and for women who want not be an occasion of sin.
It seems you are saying two things in the red. First you say that you are not excusing men with disordered minds, ie the burqa. But then you write if it is disordered for a man to lust after a woman's upper arm- she should cover it. When does this stop? There are millions of men with disordered minds. Am I to go down a check list of fetishes(sp?) every time I dress in the morning to make sure I don't tempt someone? I have been given lustful comments about the shape of my lips- where does that leave me?
In the example I gave- there is no way you are going to see her bra or any part of her breast. Period. I already explained that when I talk about sleeveless shirts/ dresses, I am not talking about immodest ones. Because there are both. Are you implying that if a woman wears modest sleeveless shirts that she will eventually wear something immodest?
Whenever my husband sees a woman dressed immodestly he turns his head and doesn't look till she's out of sight. He might say some prayer, idk. He has done this since before I knew him. He used to get very angry when we would drive by a bunch of teens in very little clothing advertising a car wash. Now, he feels sorry for them. Instead of thinking "hey there...", he thinks about the fact that they are doing this for attention and are going to end up in hell if they don't change.