I can't believe that anyone would consider benching Warner while he's healthy.
I agree. I don't believe Warner will be playing in all 16 games this year, so you want to play him while you can. Both QBs are injury risks, but the safer choice is Kurt. Don't forget that Arizona throws over 60% of the time. That's a fantasy dream.
In my opinion, there are only two players you really want to have from Houston: Johnson and/or Slaton. Putting Shaub in your starting line-up won't give you much because Johnson is his best and, usually, his only valuable option. Warner does throw it around a bit and with 1pt per 20yds, he's going to give you a bucket load of points. Think of it this way: if Fitz receives half the passing yardage with 10yds per catch and Warner uses his other two/three receivers with a combined avg. of 10yds per catch, you will neutralize Fitz's points.
Now, that's all 'what if' and I don't know what else you or your opponent has, but Warner will provide you with good stats for a QB and a chance to relax while facing a team with Fitz. I'll tell you what though, you may be suffering later on in the year with two injury risks for QBs.