It's actually not a security measure, although I can see why it could be viewed as such.

That feature is in there because sometimes Maya can save out files it cannot read back in, and often the only way to get at your data in order to salvage some of it is to disable scripts and expressions. I'm using that feature at work to debug some inherited assets because when I load them up straight Maya likes to hang.

But there's a difference between that and what Blender's currently doing: that "security" feature is opt-in. Blender's is not, but in my opinion should be.

And as an aside, that feature in Maya can be gotten around with deferred execution and a hack in a Maya ASCII file. Again: not security, but a debugging tool.

I'm surprised that nobody has mentioned the simple solution of disallowing automatic scripts and scripted constraints from accessing the os and sys modules (perhaps limiting imports to only bpy). It'd be easy enough to implement as a security measure by just scanning the code or executing the code in a space where those modules were never importable, but wouldn't break rigs.

~ C