I never said SAS is interested in Whitside. Just that the salary could match. Maybe a 3rd team would get Whitside. Or maybe Blazers would give SAS draft picks, so they don't mind the downgrade from LMA to Whiteside with that benefit. Who knows, my point was there are ways to possibly do this type of trade if teams and players want to.
This is why I cringe anytime someone mentions sign-and-trades (this isn't directed at you specifically, I encounter this daily on other social media platforms as well):
Name a sign-and-trade that happened because a team wanted another player from another team under contract and tried to get that team to sign one of their free agents just to make the trade work? It doesn't happen like that.
Sign-and-trades happen for two reasons. There were a couple instances of a double sign-and-trade last year because of two coincidences of two teams trying to sign the other team's free agent but the same reasons still applied.
1) It's a restricted free agent that the team that wants to sign them fears if they sign him to the offer sheet his original team would just match the offer so they try to work out some sort of compensation instead (See Malcolm Brogdon last summer).
2) The team that wants to sign a free agent doesn't have enough cap space to outright sign that player so the only way to sign him is via giving up salary back to the original team (See Jimmy Butler last summer).
Now let's apply this situation to the Aldridge trade. If DeRozan opts out the Spurs would have enough cap space to outright sign Whiteside. So even if they really wanted him (which I seriously doubt Pop would want a guy like him but I'll leave opinion out of this) they could just sign him. If DeRozan opts in they'd have the Full-MLE to offer Whiteside without needing to trade anyone away either. Now the Blazers can't offer Whiteside in a sign-and-trade, it has to be the team that wants to sign him that approaches the Blazers. So in order for a sign-and-trade with the Spurs to happen all of these things would have to occur:
1) DeRozan opts in.
2) Spurs want to offer Whiteside a multi-year contract for more than the MLE.
3) Whiteside agrees to that contract with the Spurs.
4) The Spurs would want to deal Aldridge for Whiteside.
5) The Spurs would have to pay Whiteside at least $19,120,000 million per year to make the trade work (if Portland included just picks) or Whiteside's first year salary combined with other salary would have to equal that amount.
6) Both teams would have to agree to whatever terms.
So the first three steps have to occur before we'd even know if they'd be willing to trade Aldridge for Whiteside. What is being suggested here (and by a bunch of other people) is backwards. Philly didn't/couldn't have gone into last off season wanting to sign-and-trade Jimmy Butler. They got lucky that the place he wanted to sign was willing to give up decent pieces back to them and couldn't just outright sign him. They couldn't have contacted the Heat and said we'll sign-and-trade you Butler, it was only after Butler had agreed to sign there.
In summary, sign-and-trades only happen because a team wants to sign a player and doesn't have the space. They don't happen because a team wants to trade for a player on another team and doesn't have the contracts to match salary.