Unpopular opinion: Charlotte Lucas
I love the discussion around Charlotte Lucas and her decision to marry Mr Collins, but while I empathise with her to a degree, I also think she makes the wrong decision for the wrong reasons.
She's in a tough situation and her viewpoint of marriage as solely mercenary is shared with other characters across Austen's novels, even within Pride and Prejudice, but I think within the novel she is shown as being incorrect, and I...actually agree.
Marriage was obviously to some extent a mercenary pursuit, with money and status as key concerns in selecting or accepting a partner. However, part of marriage is the vows. Although I'm not personally religious, it is still significant that at this time, you must swear to love your spouse before God when marrying. This is, I think, a pretty big point: most people making marriage vows at least liked or were open to liking their new spouse! It's one thing to swear a vow with good intentions that you later fail to uphold: it's another to falsely swear, and that's what Charlotte will be doing. Even without the religious element, marriage is more than a job. Working a job you hate is definitely not the same thing as being completely stuck in an unhappy relationship.
Charlotte finds Mr Collins personally "irksome" and stupid, she doesn't particularly like the idea of marriage at all, and she also believes that Mr Collins doesn't really like her, that she's just a rebound after being rejected once already. She thinks she'll be happy because she'll have a house and security--but we see from Mrs Bennet, Mrs Dashwood, Mrs Price and Mrs Smith that these circumstances are by no means guaranteed to last, especially if your husband dies or you have more children than you can support. For Mr Collins, he also doesn't actually, currently have most of the assests she's marrying him for: and there's no guarantee those assets would be in good shape when he does get them. It's better to actually like or at least respect your husband before you marry.
Frankly, it's also unfair to Mr Collins. He's a bore and not very bright, and it's unlikely he's actually fallen in love in the space of 2 days, but he seems more honest. He thinks Charlotte likes him and he actually likes her (mostly for listening to him, which blech, but it's something). Someone like the elder Miss Steele, Mary Bennet or maybe even a Miss Bates could have been happy with him and would have made him happy in turn! Charlotte accepting his proposal, knowing she doesn't and can't love him (yet making him think she does), is preventing him from finding love in marriage and I think that's an incredibly cruel consequence for being a bit stupid and boring.
Charlotte is "disgracing herself and sunk in (Elizabeth's) esteem" not because Lizzie is a romantic soul, but because Charlotte is going to be going against her own natural inclination against men and marriage, and lying before God and everyone for potential financial gain. She is making a terrible decision that shows poor morals with her eyes wide open, and is still insisting it's going to work out because hey, she'll have a house (for as long as her husband is alive).