Despite his marginal abilities, he garners a ****-ton of media attention and scrutiny heaped upon any coaching staff and organization which he is a part of.
Here's the real crux of it. Sam's looking at a 50/50 shot of making the team. This is probably a best case scenario for him. It's actually more like 30/70, with only a 30% chance of making the team because the Rams are loaded at defensive line. If he does get cut (which is not at all unlikely), the Rams are going to be accused of cutting him because he is gay. In truth, he'll be cut because he is being treated just like any other football player, though.
Sam is doing one thing for the future, though. He has taken on the "distraction" factor for any future players who come out before the draft. The next time an openly gay player gets drafted, it won't be a historic event. It'll just be another guy getting drafted.
As I said earlier, though, if Clowney was gay, he would still have been drafted #1 overall and any GM in the league would be happy to have the guy on his team. You can't simply look at this as though all players are equal. They aren't. The ultimate thing that any GM is going to ask himself is "Would having this player on our team make us more likely to win games, or will having this player on my team hurt our chances to win games?"
Sam being gay will not help a team win games. Sam being a role player/special teamer could potentially help a team win games, but having him on the squad is only going to be a slight benefit. He's just not likely to be good enough to be a significant boost to a team.
But it's also possible that the media attention Sam receives could be a distraction from actual on the field stuff, which could hurt a teams chances to win games. Like it or not, that is a distinct possibility. The GM has to weigh out whether their assessment of Sam's abilities outweigh the potential for distraction. Unfortunately for Sam, most Gm's don't think so. If he had Clowney's talent, most GM's would absolutely think his benefit to the team outweighed his distraction potential. It's a business and Sam is being treated just like any other player of his abilities would be treated if they were drawing the kind of media attention he draws. The key thing here is "of his abilities".
People keep trying to compare Sam to Michael Vick (freakish athletic ability) or Ray Lewis (one of the best ever at his position), and other "elite" player. Nobody thinks Sam is going to be an elite player who could impact games anywhere near the level those guys did. Nobody. He's going to impact games on about the same level that a Blake Costanzo impacts games.