Agreed with the bold, but I don't think this is what you meant to write. Having legitimate concerns is one thing, but then choosing a course of action that exacerbates those concerns is not justifiable. Sickles concerned about his flank, ok, but his decision creates an additional two open flanks (his right and now the 2nd Corps left). He is concerned about support, but then moves his line closer to the rebs and about twice the distance from his support. Sickles is concerned about having enough men to defend his line, but then he creates a front that is even longer. Having legitimate concerns is one thing, but when the decision you make worsens those concerns, those legitimate concerns don't justify but rather further condemn the move.
Agreed with the bold, but I don't think this is what you meant to write. Having legitimate concerns is one thing, but then choosing a course of action that exacerbates those concerns is not justifiable. Sickles concerned about his flank, ok, but his decision creates an additional two open flanks (his right and now the 2nd Corps left). He is concerned about support, but then moves his line closer to the rebs and about twice the distance from his support. Sickles is concerned about having enough men to defend his line, but then he creates a front that is even longer. Having legitimate concerns is one thing, but when the decision you make worsens those concerns, those legitimate concerns don't justify but rather further condemn the move.
Except, Sickles was not worried about his flank
per se but the defensibility of his position in general.
The position, unlike Union positions further North, which had the advantage of the high ground of Cemetery Ridge, was dominated by a high plateau on which the Peach Orchard was located.. With growing evidence that it was or soon would be occupied by the confederates.
As I have noted before, the movement can only be assumed to have been an error, in the absence of any evidence that there would have been a better, resulting in a better result than what actually happened. As I have also noted, the history of the War up to that time would indicate a coordinated confederate assault on the Union Flank, which was exactly what Lee planned, had a much better chance of success than not.
In point of fact, I do not think III Corps or its reinforcements were ever outflanked. Longstreet's attack was stymied even as it began and what had been planned as a coordinated assault on the undefended Union flank, a staple of many ANV victories, and became a head on infantry battle,, a style much better suited to that of the AoP.
Instead of moving to the North as had been intended by Lee, Hood's Corps was forced to move sideways to the East looking for the Union flank, negating almost all forward movement.
The end result in the end, was that on Day 3, Lee had only a fresh Division, while Meade had a fresh(or at least more fresh than his others) Corps.(that Meade did not take advantage of that fact, was not Sickles fault.
My point is that a planned and coordinated Confederate attack on the Flank of the AoP, was turned into a stubborn infantry battle, that yielded a better result, than could have been expected from receiving the assault as planned by Lee. It is sheer speculation to assume another action of Sickles(or Meade) would have yielded better results, in the light of the history of the War and experience of the AoP, up to that time.