Odd behavior of sensible people

This observation applies to Austen's book and all adaptations.

I find Col Brandon's "withholding" Willoughby's seduction and abandonment of Eliza from Mrs Dashwood to be very questionable. It seems self-centered, ungentlemanly and even stupid.

Let me explain. What is the reason given for not saying anything before the engagement of W to rich woman is known? One, he thinks no one would believe him and might think him just trying to say mean things about Willoughby because of jealousy. And, two, somehow he thinks Marianne might "reclaim" Willoughby. Now I'm a great fan of suspended disbelief. You almost have to be able to do that to enjoy most movies. But if you think about it, his reasons for not telling aren't very well thought out.

He was worried no one would believe him. Well, when Eliza AND THE BABY came to live with him and vouched that it was Willoughby that "did it" then he'd be exonerated. Willoughby's rich relation ALREADY is convinced he did it, that's why he's disowned. So there's no denying it from that side. I don't think even Willoughby denied it. If he had...he could have just denied it...to everyone including his rich relative, Eliza, Brandon, everyone. After all, it's just her word against his...I mean they didn't have DNA testing then. So what's the problem?

And EVEN IF NO ONE BELIEVED HIM, Brandon still has a gentlemanly duty to be honest and notify his good friends of the pitfall Marianne is about to get herself into. He could have arranged a meeting with Mrs Dashwood and simply explained it. I'm sure a real Mrs Dashwood would be eternally grateful. Let's imagine if he had mentioned it to Sir John M. Can you imagine for a second Sir John would have agreed..."oh, sure Brandon keep that a secret, think what it would do to YOUR reputation if no one would believe you." THinkwhat Mrs Jennings would have thought..."you kept THAT from our good friends and relatives, the Dashwoods?" I am amazed Elinor takes it so...gratefully. "Oh thank you...FOR WAITING TIL NOW TO TELL US YOU CREEP."

Then this absurd notion that he thinks Marianne might "reclaim" Willoughby. First, why is it the task of a decent woman to "reclaim" anyone. Doesn't each woman have the right to pick someone with good character rather than be obligated to take the scum of the earth and reclaim them? What's Marianne going to think of Brandon from there on out when, and I mean WHEN the truth comes out?

Second, the "reclaim" line of reasoning is doubly stupid coming from Brandon...HE ALREADY TRIED THAT WITH ELIZA THE SENIOR. He "left" England thinking it might help "save" a marriage. A marriage where, by the way, brother was already treating Eliza cruelly, but Brandon left anyways. And he saw how that turned out. Eliza the senior fared poorly under that treatment, so why'd he think Marianne would do any better?

So, I am puzzled why Austen wrote Brandon that way. Does anyone have any idea? Is it just a good story that was not well thought out? That's a pretty sad way of thinking of Austen. Or was Austen teasing us by saying he's a really honorable, good guy, but he's dumb as a post?