Honor, duty and propriety are very important to the heroes and heroines in all of JA's works. I love the expression "manacled to the past." That is very true. Still however propriety prevents either Anne or Wentworth from doing whatever they darn well feel like. And a good thing it is too. It would not be half so interesting for the reader if they did what they liked whenever they wished as the novel, would be about 80 pages long. Or perhaps might not even exist because without her sense of propriety and duty to Lady Russell, Anne might have never been persuaded to give up the engagement in the first place, or she might have gone against taboo and convention and sent Frederick an impassioned letter of regret.

I think the point is that we would live in a disordered and chaotic world we would have if there weren't people like Anne and Frederick who were willing to put what was expected of them by society above their own desires. If everyone were as selfish as Sir walter, Louisa, Mr. Elliot, Mary, etc., etc. life would be unbearable, because while those people are amusing to read about for an hour or so, would you really wish to be related or (gasp) married to one.

I agree though, it is delightful to read about the people who are less disciplined and move outside this code of ehtics. JA seems to relish writing those characters and knows full well that we take guilty pleasure in sometimes liking them more than we really ought.