Two points Dick, there's nothing stopping an aircraft requesting headings to avoid - the pilot is responsible for terrain avoidance as we'll be saying "suggest heading". What makes you think vectoring is a good solution? It's not when you have absolutely no idea what the mystery aircraft is doing. Levels is far safer - aircraft routinely make sharp turns but don't tend to change level abruptly.
Don't listen and you may get unlucky - I've been thanked a few times by pilots for saving their necks. It's an extra tool in the arsenal to avoid each other.