Luigi Mangione's Sex Appeal Due to Robin Hood Bad Boy Fixer-Upper Combo, Doc Says

Even before a suspect was identified, people were cheering the UnitedHealthcare CEO killer ... but it went to a whole new level when a face was finally seen -- and admirers' parts started to tingle.

Here's the deal ... Luigi Mangione was apprehended Monday ... and hours later, the Manhattan D.A. charged him with murder in the brazen December 4 fatal shooting of Brian Thompson.

Renowned sex doc Laura Berman tells TMZ ... women have found notorious criminals attractive in the past -- Ted Bundy being a classic example -- but she's never seen the thirst level that's been on display for the suspect Mangione.

Not only is Mangione seen as physically hot ... he's also perceived as a Robin Hood of sorts and the ultimate fixer-upper … which Dr. Berman tells us sends his sex appeal through the roof.

For some throwing around the peach and eggplant emojis ... they might not even be aware their lust is also driven by biology and evolution … Dr. Berman explains that women are more attracted to “bad boys” ... 'cause they're risk takers -- meaning they're perceived as bold hunter-gathers and protectors.

As we reported ... Etsy has pulled a lot of items with Luigi's infamous face ... fan-made merch flooded the e-commerce site after his arrest.

GoFundMe also recently removed all campaigns created for Mangione ... telling TMZ they violated the rule of not seeking money for legal defense of violent crimes.