In my opinion, in the context of that post (with the upskirt photo), your comments are wrong in both respects.Showing an upskirt shot of a pair of startlingly-white knickers, whilst possibly "educational" (in a sense) does nothing that couldn't have been said in a narrative, and really doesn't say anything that any of us weren't already aware of (at least those of us with some modicum of modesty); what it does say, however, is that flashing one's knickers in public may be acceptable, or at least titillating to others (it's not: even on pretty women it's vulgar).
1) It did make a point that could not have been made in a narrative - as the photo was a visual example of the point being made - about posture while sitting. Although most men who wear skirts would already be aware of the need for care when sitting etc. the photo was a good example of the fact that even though you may be very careful, you may nevertheless be sat in an indecent fashion without being aware of it.
2) The post concerned (with the upskirt photo) certainly did not in any way say that flashing ones knickers in public may be acceptable or titillating. I'd like you know where you got that interpretation from - because that was not my perception of the post or the photo. In fact, the poster made clear from the start that he was only posting that photograph in order to illustrate a point.