The Lincolnshire MP is the first senior Conservative to openly attack his Party’s opportunist behaviour in the House of Commons.
Cameron instructed his MPs to support an unsuccessful motion by Scottish and Welsh nationalists calling for an inquiry to be held while British troops are still in action.
Quentin, former Tory defence spokesman, abstained from Tuesday's vote.
Thanks to Ridiculous Politics for picking on BBC Radio 4's Week in Westminster report
Quentin told the BBC he could not understand why anyone, especially his party, would vote for it. He said:
"I was quite incredulous when I heard we were going to vote for that [SNP/Plaid] resolution.He said it would be unprecedented to hold an inquiry during a military campaign.
I didn't vote for it but most of the party did. [That] left me really quite amazed and I'm very sorry about that as a matter of fact.”
To have an open inquiry would be
"signalling to the enemy all your plans and all your weaknesses...That can't make any sense at all, and I think that soldiers serving out there in these very difficult conditions would have been just as amazed as I was."He said the party should be careful to base its actions on "analysis of national interest" and not to give the "slightest sliver of suspicion" that it was playing "party politics with these serious issues".
But Mr Davies added the credibility of the party as an alternative government would be seriously damaged if it gave the impression of "cynically" shifting with the prevailing party political wind.
Another senior Conservative who was absent from the crucial vote - but who declined to be named - described Mr Cameron's decision as "intellectually and morally indefensible".
The MP suggested a number of Tory MPs were deliberately absent. And the BBC reported that there are suggestions that the issue has caused splits within Cameron’s cabinet.