The cynic knows the price of everything, but the value of nothing
He got cut from the Panthers and the Cardinals let him walk. Keep in mind, the Cardinals let him walk after he played at least part of the season at a position better suited to his talents: safety. As the Panthers had been slowly building back up their defense(and now offense) and the Cardinals are completely rebuilding, that neither team wanted him back is telling. Its easy to say Marshall had a bad year because he got injured, but even before his injury he was a liability. Between regular season and preseason, he played in 8 games(7 if you want to discount the final preseason game, which he played but not for long). He wasnt good. Anyway you want to cut it, he was adequate at best...and thats a bit of a exaggeration.
Even if we keep him, we still have a hole at corner. You cant keep bad players just to have a roster spot taken. There are to many decent players just waiting for a chance to play to justify holding onto a bad player. The fact that those players would not be asking for $6 million a year is also incentive to get rid of him. And holding onto Marshall just because you absolutely screwed up in the past(example: trading Vontae, relying on Smith) is the epitome of idiocy. Its making a bad situation worse. Ireland screwed up with signing Marshall to that big a deal. Continuing to pay bad players in order to save face is one of the reasons we keep losing.