Seeing Iginla in an Oilers jersey would forever alter my perceptions of him, and I think that's normal. You cheer for a team -- that's not necessarily rational, but you do it, you adopt the colours, the culture, you learn to dislike your rivals. That's part of what sport is about. Its civilized war in some respects. Loyalty is part of the equation when it comes to sports.
Imagine a world where Gretzky at any point of his career signs with the Flames. It would ignite a lot of passion, mostly negative. It is that very passion which drives the league and its revenues. We pay big bucks to go to the games because they are exciting to watch and because we care about the players and the persona they bring to us, wearing "our colours" and providing a sense of shared pride when they win. Losing teams earn less ticket revenues, Leafs notwithstanding
So should Iginla ever sign with the Oilers, so be it, and I wish him the best, however, I'll be among those who drops him down a few notches on my favorite all times Flames list. As in, from 1 to probably around 10. And that doesn't matter to Iginla as a I am a lone insignificant fan, but as a fan I follow my team, and Iginla signing with the Oilers even in his late career would alter my view of his tenure with the Flames.