It's no secret that McGwire wants to be a manager. Being a hitting coach is a very good way to do that. But, I think LaRussa wanted him to be the hitting coach contingent on him coming clean- or rather clearing the air about the situation. Tony LaRussa and Mark McGwire have a very close relationship, and I really think that LaRussa wants what's best for him. And in this case, I think Tony felt like that was coming out and talking about steroids- whether he did them or not. I really think that LaRussa expected him to deny using them, but if he did, I don't think anyone would buy it. I know I wouldn't.
I think in the long run it will benefit McGwire, and I'm not talking about the Hall of Fame either.
Plus, I seriously doubt that LaRussa or anyone else with the Cardinals wants a big distraction from all of this at any time other than spring training. This is going to be a "story", but much like A-Rod, I don't think it will drag out all season long. Go ahead and come clean, let people talk about it for about a month, and get grilled in spring training when no one gives a crap, and then move along.