If he has done so, then your line of argument is consistent and honest. If he has not, then there is something else at play, and your argument sounds remarkably like the myriad of "desperately seeking something to object to" posts which pervade these discussions.
Which is it?
Romney has not done so; he's basically taken the Bush line on it, which is better than most of the others but still not great. I'm supporting him because, so far, he's the closest match to what I'm looking for, with Thompson as a close second. But such a declaration from Thompson - or anyone else - would put them over the top for me. Unfortunately nobody in the race has had the courage to say it yet. I fail to see how this is inconsistent or dishonest.
With your clarification which I underlined above, that's a fair enough answer. As long as you are applying that criterion to all candidates equally it negates the appearance of inconsistency.