It can also be argued that Austen also shows her disapproval about marriages for the wrong reasons through the way Lizzy observes her parents' marriage.  While we don't really know why they married in the first place, they are clearly ill suited to be together.  Mrs. Bennet is silly like her daughter Lydia and a bit "low class" both in her manners and in her upbringing.  Mr. Bennet is much more scholarly and prefers to be locked in his study with his books, avoiding all of Mrs. Bennet's machinations for her daughters whenever possible.  The two seem to care for each other in their own ways, but they are often disagreeable towards each other.

The end result of their ill suitedness for each other is Lydia's scandalous elopement.