That is correct (prevent accidental script execution).

It is ABSOLUTELY NOT a security mechanism. That is why we we support this:

Set-ExecutionPolicy -ExecutionPolicy Bypass

I wanted to make it:

Set-ExecutionPolicy -ExecutionPolicy DoAnythingBecauseTExecutionPolicyIsNOTASecurityFeature

But the team didn't like that. (I should have overruled them on that one :-) ).

Jeffrey Snover [MSFT]