What is the problem some people still have with Camilla? Why the continuing secular beatification of Diana?

Diana was undoubtedly a victim. A victim of her familys' ambitions. The Spencers/Despensers have had their eye on the Throne ever since the 1st Baron Despenser crawled into bed with Edward II in the 1300s. That ended with Despenser being hanged, drawn and quartered and Edward II getting a red-hot poker up his bum! They actually had to quietly reverse a 14th century law to allow Charles and Diana to marry because of it.

Charles was also a victim. A victim of his family and his 'duty' to marry and produce an heir. The combination of a naive, rather silly young woman who demanded constant attention and an older, workaholic man with an unbending sense of duty was inevitably disastrous.

As Queen, Diana would have continued to be demanding and needy. She would have gone on demanding support from Charles and never giving him any. Queen Camilla, we know, will support Charles as well as standing between him and other people whenever he starts channeling his father!