I guess it's the way he's symbolic of the change in what a footballer is. Primarily, he seems to be a professional celebrity and a part time footballer, which seems more like a hobby. I think my venom towards him was really created by Sven Goran Eriksson, and his bizarre obsession with him. This extended to other players (Gerrard and Lampard together for example) but Beckham seemed to be the apex of the problem. He was never substituted when his trick (singular) wasn't working, and created a horrible imbalance in the midfield with his constant deep positioning and desire to come inside to an already crowded area (Joe Cole does this too).
In terms of his two strengths, there are players who can deliver crosses just as well (his best mate Neville has done some great ones from overlaps), and free kick-takers with better hit rates and greater variance (Sinisa Mihajlovic, Ronald Koeman, Gianfranco Zola, Krassimir Balakov). There has always been far too much focus on these two things, without people ever really recognising his obvious weaknesses.
That's what I suspected might be the case but in truth you're conflating two, IMO, distinct criticisms there. There's the angle of his worth as a footballer and the angle of his celebrity and it's easy to see why one would try and merge them together. That is after all how he managed to build his cult and his wealth.
But I still think that Beckham has been, on balance, our best footballer of the past decade. Fair enough, he has a limited range of ability but what he can't do (beat a man) he makes up for in his undoubted work rate and specific skills. I think there's a couple of things to bear in mind here. Is it valid to blame England's perceived underperformance principally on Beckham and was there anyone else good enough to come in for him?
I think the answer to both those questions is categorically no. In 2002 we were fielding people like Danny Mills. In 2004 our only effective forward and point of reference for the whole of our attack was injured early in a crucial game. And in 2006 the entire team looked like they'd forgotten how to practise their profession. In point of fact, although Beckham was not good in 2006, he was a long way from being our worst performer. Furthermore the only reason we were at 2002 was because of Beckham.
Then lets look at the alternatives. I cannot think of a single candidate right now, or in the recent past, in the whole of England who could justifiably be labelled as an international right midfielder or right winger. Despite what the FA's marketing men would have you believe, we had and still do have a very limited pool of talent to choose from and none were, or are, better than Beckham in his position.
Beyond that I think you have to look at his record at club level. He was a crucial part of a superb United team who fielded one of the most effective midfields in recent memory. That is no mean feat.
In successive seasons he was the only reliably effective member of an incoherent, bloated Real Madrid side. Ironically you level the accusation that he forgot he was a footballer first and foremost. During his brief time as a Galactico, it's more than possible to argue that he was the only Galactico who remembered what being a footballer meant and how to go about it.
In his final season he was dropped for alleged disloyalty and then regained his place through unstinting professional standards and demonstrable excellence. Qualities that managed to change the mind of a manager (Fabio Capello) who is famous for his readiness to undermine and cast out 'stars' who he believes do not have the focus or the committment to the team.
History will surely judge Beckham as our most successful footballer of the modern era, and not just for his trophy cabinet. The fact that he made an awful lot of money doing things that you may find morally or socially dubious shouldn't obscure that.