I used to work for Macromedia - from 1995 - 1998. I was there when they bought Flash (It was called "FutureSplash") and yes, it was originally supposed to simply do vector based animation, because bandwidth back in the mid 90s sucked balls. Fairly quickly it became painfully obvious that Macromedia's flagship product, Director was doomed. Director did pixel based animations and a lot of other things thanks to its programming language, Lingo. A HUGE portion of the development cost for Director went into Lingo. Now with Director made (mostly) redundant by Flash they had to figure out what to do with the people. So, what better way to fuck it up than to shoehorn some crazy language into it and give it superpowers like Director? Enter ActionScript.
There was no reason to think about security - it was a tool to make stupid games and animations on the interweb thingie. And, like Director it became increasingly bloated and complex and pointless. Flash was dead long before the security gremlins appeared. Then Adobe bought the whole mess, hook, line, and sinker. Suckers. Between the headache that was Flash and the eye watering bilge that was ColdFusion, Macromedia got even with Adobe by serving them a hot buttered plate full of digital poo. The only thing, IMHO, that was worth a right flying fuck from Macromedia that Adobe got was FreeHand, and, Adobe, in it's infinite wisdom, killed FreeHand, even though it was a demonstrably better product.
Macromedia was poorly run by a bunch of wolverines. They got bought by the Borg. And now there's basically nothing left of value except Photoshop, After Effects, Premiere, and inDesign. And I'm not that certain about Premiere....