“Tap the brakes” is a term used all the time on this board by many. It’s used in the media. You’re taking it way too literally. No one is telling anyone what to do.
Here's your original quote:
I’m fine with fans pulling for Aldon Smith but those who are getting all worked up about the potential of our pass rush with him and Gregory who has yet to be reinstated better tap the brakes.
Tap the brakes means you are telling them they need to slow down. If you are not clearly saying, "You people getting all worked up better slow down," then what are you saying? Because them's what the words mean.
As I said, if they want to get worked up, then let them. I'm excited about the possibility, but at the same time realize that it might not work out for either Smith or Gregory. That doesn't mean I'm going to suggest that others who are all in shouldn't be. I'm fine with fans pulling for Smith and also getting all worked up about the potential. Either way is their prerogative.
I just don't understand the need to tell fans how to feel. I'm sure I've done it more than a time or two myself, though, so I'm not trying to be rude about it. Just pointing out that it's unneccessary.