You Just Don't
Let's start with history. Karl Malone played 18 seasons with the Utah Jazz, who were the Spurs chief rival in the old Midwest Division. In fact, during David Robinson's career, a team other than the Spurs and Jazz won the Midwest Division exactly twice. The Jazz knocked the Spurs out the playoffs in 1998 (4-1), 1996 (4-2) and 1994 (3-1). Those facts alone are enough for every Spurs fan to hate the Stockton and Malone Jazz. But there's also this one other little fact.
Karl Malone tried to kill David Robinson on March 8, 1998. Malone had his back to the basket with The Admiral right behind him, hand in his back. Malone, certainly knowing where David was, whirled with his elbow up. He caught Robinson on the side of the head, knocking him unconcious. Robinson twisted his knee as he fell and lay motionless for 2 minutes. He ended up staying the night in the hospital and missing three games. Malone, despite being widely regarded as the dirtiest player in the league, got a measly one game suspension. How could the Spurs sign a guy who tried to maim the franchise's most beloved player? (Did you know that Karl Malone actually ended a guy's playing career while in college? See the the previous link for more info.)
Would Spurs fans even cheer for the guy? I've been to a Spurs/Jazz playoff game, and the one thing I remember is the undeniable group hatred for Malone. He was booed when he touched the ball. When he was at the free throw line the fans, in unison, would count out the seconds as he stood there, mumbling to himself.
And don't say "What about Robery Horry?" Yeah, Horry was part of a couple of Laker squads that took out the Spurs, but he was way down the list of hated Lakers. He wasn't even in the first tier. That's Shaq followed closely by Phil Jackson and Derek Fisher.
The above is enough to squash any thoughts of adding Malone. But, just to cover all the bases, let's talk about what he would add.
Seriously folks, do the Spurs need another guy totally unwilling to shoot the ball in the playoffs? Did anyone even see Malone in the post season last year? He passed up just about every wide open 18 footer. I think Mark Madsen looked for his shot more. Malone is a virtual zero on the offensive end.
He still has something to offer on the defensive end. Time and time again the NBA refs have shown an unwillingness to blow the whistle on Karl. Consequently he shoves around whoever he's guarding. But who's he going to guard? Who are the Spurs going to face in the post season?
First Round -- Memphis, Houston or Minnesota
Yeah, he'd be good against Yao. But Yao is slow footed and not exactly a power player. Nesterovic would be at a disadvantage, but Yao wouldn't go for 30 against him. Memphis has Gasol, but come on, we're not worried about Memphis are we? Minnie has Garnett, who would shred Malone. Malone needs to guard someone he can intimidate (like he did to Duncan last year). Garnett is not that player.
Second Round -- Sacramento, Dallas or Seattle
Sacramento has Webber, but all he does is shoot 18 footers and pass the ball. Their offensive threats, the guys who need good one on one coverage, are Peja and Bibby. Dallas and Seattle play small ball. The Spurs would probably play Horry at the 4 spot against those teams.
Conference Finals -- Phoenix
Malone serves no purpose against these guys. Who the hell would he guard? Stoudemire? That's laughable.
Finals -- Miami, Indiana, Detroit
Here's where it gets dicey. The Spurs don't have anyone to guard Shaq. Nesterovic got eaten alive last year. Shaq is the exact type of player Malone could still be effective against, and Malone would be good against Indiana's O'Neal, too. I cannot simply discount Malone's value in this scenario.
However, I don't think the Spurs need another piece to win it all. Malone's one relevant positive ability is his perceived ability to slow down Shaq or Jermaine, but that doesn't come close to outweighing everything else.
But that's not the point. I, and I think most Spurs fans would agree, would rather not win the title than win it with Malone. The Spurs have never been a win at all costs team. They've never mortgaged the future to win in the present, and they almost always take into account the character of the player, how the player would fit, how he handles himself, how he reacts to coaching, how he fits in the with the people of San Antonio.
Just don't. You just don't. Please. Keep the team clean.