Alesha doesn't have the technical knowledge of the other judges, but my line of though is that the celebs are the ones being judged, not the pros and I feel the emphasis will be on this for Alesha. As this years' celebs won't have any more time than Alesha had to learn their routines and steps, surely in general they will not be at a more proficient level than Alesha was when she competed, and therefore she has enough knowledge to give some sort of overall basic judgement? I know Alesha didn't execute everything in a fantastic way technically, but that doesn't necessarily mean she doesn't know how the steps/moves should be done (in general terms), just that she didn't always manage it, and for me, she was certainly a great performer.
I can totally see how those with dance experience feel it's a dumbing down of the show, and why so many people are upset by the decision. Plus, if the pros are being judged by Alesha directly, that will indeed be something I am completely against, but if Alesha keeps her focus entirely on the celebs, I don't see why she can't make a good contribution to the show and give her honest opinion at the same time. This is not to say I agree with Arlene going, that is a separate matter from what I'm talking about on Alesha alone.
This is not the role I would have chosen for Alesha, but I can't imagine she would presume her technical knowledge is sufficient to judge the pros or that she would even want to do that, and I think/hope she will balance her judgements accordingly. (Then again, I could be talking complete bobbins, because I know next to nothing about dancing, and usually vote for my favourite partnership whatever


)