Been saying it for years - that wasn't really a bad decision at all when you take everything into account. And there was a reason for it - the Steelers had just pulled to within five and a two-point conversion at that juncture of the game puts the Steelers behind by only a FG (28-25 instead of 28-24). After being behind by 18 going into the 4th quarter of that game, they were after every point they could get.
Tomlin only gets flak for it because it failed on the second attempt at it. And if Mahan hadn't gotten called for holding, it would have been good on the first attempt.
On that note, it would be interesting to go back and account for just how many times one of those shitty O-linemen we had back then cost us points with a stupid penalty.
Oh, and
speaking of shitty O-linemen...
So, considering the typically "stellar" OL play by the Steelers in that game which was pretty much a hallmark of the team during that season and for a number of seasons afterward, it was anything but a sure thing the Steelers were going to score another TD after that, or even score again at all, so trying to pull within 3 with the two-point conversion attempt was the correct move at the time.