First of all to bring some sanity back to this conversation, let's clarify exactly what we're talking about here. I believe we're talking about Boykin simply starting this 1 game -- a 1 and done and that's it -- not the entire season. If that's what we're talking about here (given the current physical state of Russell Wilson), then I think it's certainly something you have to consider. Russell is a tough guy (as we'd all admit), but I think Carroll would even admit that there are times that Wilson needs to be protected from himself. Sometimes the smart thing (though it's hard) is to sit one out to give yourself time to heal up because in the long run, it's going to hurt you and the team worse if you don't.
Anyway, back to the OP's original question, "Why can't we win with Boykin?" Now, if we were going up against a team like the Patriots or the Packers (teams with good to great starting QB's) -- then fine, I'd concede that we would need Russell Wilson to win. Absolutely. In this case however, I believe it's possible. Take an in depth look at this particular opponent in the Jets and I think a case can be made for the idea of starting Boykin here.
First of all, Boykin's opponent doesn't exactly have a history of lighting it up as a QB. In fact, quite the opposite. The Seahawks under Pete Carroll have faced Ryan Fitzpatrick twice -- both times pretty much owning him.
The first time that the Hawks faced Fitzpatrick was back in 2012. He was the Bills starting QB in that epic 50-17 blowout of the Bills. While he did throw a TD, also threw 2 INT's, had a fumble, and was sacked 3 times.
The next year in 2013, Fitzpatrick was a member of the Titans and faced us in Week 6 (10/13). In that game, he again threw 2 INT's (he had 0 TD's), had 2 fumbles, and was again sacked 3 times.
While it's admittedly a very small sample size, Fitzpatrick hasn't exactly lit it up against the Seahawks. He's struggled both times. Given that he struggled against a very good defensive team in Kansas City, it's fairly reasonable to expect he's going to have his issues against the Seahawks. He's also fumbled in each of his first 3 games, so if that's any indicator of things to come, it would appear that there will be turnover opportunities to be had. The Jets are heavily dependent upon their run game to open things up for Fitzpatrick. Stopping the run is what the Seahawks absolutely excel at, so I don't see the Fitzpatrick and the Jets lighting up the scoreboard in any way, shape, or fashion. I'd predict quite the opposite.
Flipping over to the other side of the ball, that defensive line is arguably one of the very best in football. Most of the attention has been focused on guys like Muhammed Wilkerson and Sheldon Richardson. They could be problematic and potentially be chasing our QB's all game long (which is why I think sitting a less than mobile Russell Wilson may be the prudent move here).
The reason why I believe Boykin could have some success in this game is that Jets secondary. They are Night and day different from their front 7.
It's early obviously, but as of right now, the Jets are statistically one of the WORST secondaries in the NFL.
Through the first 3 games, the Jets are allowing ...
71.3% Pass Completion% (Worst in the NFL)
an average of 9.7 yards/pass attempt (Worst in the NFL)
a QB Rating of 110.7 against them (2nd Worst in the NFL)
they have allowed 6 passes of 40 yards+ already (tied for 2nd worst)
an average of 284 yards/game passing (21st in the NFL)
Many people are starting to question whether or not Darrell Revis is starting to show his age. Whatever the reason, teams in the early going are having success against that secondary. If Boykin were to go in there with a game manager type of script, I think the chances are good he would come out of this one with a W.
For this one game only, given all the various factors, I think starting Boykin is at least something you have to consider.