I don't think there's a problem in pointing out holes in a programme, because that can be a bit fun to do, the problem is that some damn a programme due to minor ones, which can well be seen as petty. I like to spot holes in things, it's just a bit of fun to me, but I tend to forgive programmes where there are minor issues and just allow some suspension of disbelief, etc. Obviously, if the holes, mistakes or wrong mannerisms get a bit too much, then there's something wrong to moan about, but I don't think Downton Abbey has got to that level yet.