How does Malone's character differ from Stack's?

Dorothy Malone's character is often described as a nymphomaniac. We see her drink at a local roadhouse and pick up men for (what's presumably) one night stands. We're supposed to feel some sort of condemnation toward her, just as the Rock Hudson character does.

Yet her brother shows up for business meetings drunk, and proposes marriage to a woman he's just met that day...after trying to lure her into bed with a shipment of magnificent clothes and a hotel suite. Rather than condemning him, Rock Hudson stays his best friend.

Which one is really the more unstable? Isn't it actually less of a problem to sleep with someone you've just met, versus proposing to them?
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