As Muriel pointed out in this thread, all but one MP voted against the proposed legislation and so they are essentially in agreement with him -he's not being denounced as barmy because he holds those views but because of the actions he has taken in resigning his House of Commons seat
Davis is on the right wing of the party -he supports the re-implementation of the death penalty and he voted against repealing Section 28
http://en.wikipedia.org/wiki/Section_28 in relation to homosexuality. David Cameron, the current Tory leader, is to the left of him politically. Davis was Cameron's opponent from the right in the 2005 leadership ballot that elected Cameron as Leader
His colleagues are denouncing him for predominantly two reasons:
1. The Brown government and the governing Labour Party are deeply divided over the proposed legislation and the Tories had good reason to believe that this could work to their advantage in the coming weeks and months. Many Tory MPs perceive that, by resigning, Davis has undermined the political capital that the Tories could have gained from the Labour Party's division over the issue and has instead ensured that there is an unwelcome focus on the Tory Party and the leadership of David Cameron
2. The move is widely seen as a ploy by David Davis to boost his status as a future leader in the party at the expense of Cameron. Many perceive rightly or wrongly that he is placing his own political interests above those of the party