If the Dallas Cowboys don't pick an offensive lineman in the first round of next month's NFL draft, their fans officially have permission to quit.

Seriously, this would be last-straw territory, folks. It's an excuse to follow through on all those threats you've made over the years while pulling out your hair and wondering what Jerry Jones was thinking. You would be free to exercise any form of peaceful fan revolt. Boycott the season. Picket the games. Throw out all of your blue-and-silver gear and go be a Redskins fan. Robert Griffin III played college ball in Texas. You could sell it to your friends and family. And they'd have to understand. You just can't keep throwing your heart and soul and disposable income behind a team that insists on refusing to get it.

The decision earlier this week to designate defensive lineman Anthony Spencer as their franchise player crystallized the Cowboys' most significant need at this point. Before that, you could have made the case for a pass-rushing defensive end, or even a defensive tackle, at No. 18 of the first round. I'd have disagreed with you, believing that the offensive line was the more pressing of the two lines for Dallas to address, but I'd have had to acknowledge that you had a case.

Not anymore.

Offensive line is the No. 1, 2 and 3 need for the Cowboys right now. Heck, you can make a strong argument that they need to upgrade at four of the five starting spots; 2011 first-round draft pick Tyron Smith at left tackle is the only one about whom you feel good for the present or the future. And that's the key thing to remember here -- that picking an offensive lineman in the first round is vital not just for the 2013 season but for the long-term health of the Cowboys.

What you see on the Cowboys' line now is decay, a result of years of neglect. Smith was the first offensive lineman they picked in the first round since 1981. I did the math on that. That's 30 flippin' years. If you go 30 years without drafting an offensive lineman in the first round and offensive line is consistently one of your most crippling weaknesses, eventually the light bulb's going to go on, right? This is not something the Cowboys can keep patching together without eventually adding some elite talent. If you do that, you end up having to give Phil Costa a two-year deal and deciding whether it's worth giving Mackenzy Bernadeau another season to show you something. That's not a pleasant situation.

Adding another first-round-caliber talent on the line, be it at guard or right tackle, would be a critical step in an important new direction for the Cowboys. They have, for several years now, boasted elite-level skill-position players on offense but have been unable to get the most out of them because of poor line play. They are squandering the prime years of players like Tony Romo, Miles Austin and Jason Witten -- and so far at least one otherworldly year from Dez Bryant -- by persistently failing to address this glaring need. The Smith pick in 2011 showed that maybe some things are changing, and that maybe this is becoming the priority it needs to be. Picking an offensive lineman again on April 25 would go a long way toward backing up Cowboys fans' hope that such is the case.

The opposing argument right now appears to be safety, because they also cut Gerald Sensabaugh the day they franchised Spencer, and because it looks as though Texas' Kenny Vaccaro might be there at No. 18. But come on. They aren't using four substandard players at safety on every defensive play. They are using four substandard offensive linemen on every offensive play. It's the far greater need, and again -- not just for this season, but for the long term. You build through the draft and you build through the lines. The Cowboys have to do both, and they have a good chance this year to do so.

People have been asking me all week, as I've preached this first-round-lineman gospel, why the Cowboys should "reach" for an offensive lineman if one isn't there at 18. My answer is that they won't have to. There are five offensive linemen -- three tackles and two guards -- in the top 10 on Mel Kiper Jr.'s latest Big Board . Only once in the past 15 years -- 2008 -- have five offensive linemen been taken in the first 17 picks. One of these guys will fall to 18, or far enough that the Cowboys can move up a spot or two without sacrificing their second-round pick this time. And if not, Mel's got Alabama tackle D.J. Fluker at 21. Not exactly a "reach," especially considering how vital is the need.

The Cowboys probably won't be in a position to get tackles Luke Joeckel or Eric Fisher, or even Lane Johnson. But wouldn't a guard like Chance Warmack or Jonathan Cooper look good on that line next year? And for the next 10 years? Pick that guy, plug him in and cross one gigantic worry off your list. It's a no-brainer at this point.

The Cowboys have gone 8-8 in each of the past two seasons. They have a lot of needs. And no, they can't address all of them with this year's first-round pick. But they can and must address the biggest. If they don't, it will be impossible to defend their decision.