Question

Is there a PHP built-in function to unset multiple array items by key?

That would be a native equivalent of:

foreach($badElements as $k) {
    unset($allElements[$k]);
}

or, even better:

$keys = array_keys($badElements);
foreach($keys as $k) {
    unset($allElements[$k]);
}

Answer 1

You could create an array of the keys you want to remove and loop through, explicitly unsetting them.
Examples:

$removeKeys = array('name', 'email');

foreach($removeKeys as $key) {
   unset($badElements[$key]);
}

Or you could point the variable to a new array that has the keys removed.

$badElements = array_diff_key($badElements, array_flip($removeKeys));

or pass all of the array members to unset().

unset($badElements['name'],  $badElements['email'])