There is nothing wrong with Harper Beckham she is a perfectly nice and normal child.
Her problem is that she has two parents who since the time she was born have continually allowed her images to be made public. You only have to Google her name to find umpteen pictures cataloguing her life from her earliest days until now. The same goes for her older siblings as if collectively they are all part of the brand. D&V have enough nous presumably to know that there are some very nasty trolls around, which begs the question why such high profile celebrities expose their very young children to scrutiny and possible ridicule when they can't make that informed decision for themselves. Growing up can be a difficult process there is often a gauche and awkward phase, there are mistakes and lack or errors of judgement it's not always a smooth path to adulthood, I can't see parents who expose their children in such a way are acting in their child/ren's best interests.
There are others who do it too, Katie Price is another example, many don't though, try Googling for example pictures of the children of A listers, such as Kate Winslet, Daniel Craig, Cate Blanchett, Adele to name but a handful and many more, you will be hard pressed to find pictures of offspring, because quite rightly I imagine, they take the view that they may have entered the public arena, but their child/ren haven't. It is a different matter of course, as in the case of Tilly Ramsay on Strictly, presumably as a young adult she has made that choice herself.