This is a real old chestnut. Every Women's Society at every university in every year since 1978 has made a speech that includes the statement "All men are potential rapists".
It is a phrase first coined in Marilyn French's feminist classic novel "The Women's Room", by the mother of a young woman who has been raped. (Though I doubt most students these days realise that!)
It's a piece of polemic - a rhetorical claim - just like "Meat is Murder" and "The only good Tory is a dead Tory" and "All animals are equal, but some are more equal than others". 
Like other rhetoric, it contains some truth, yet is not entirely true. People who say it generally mean to highlight some facts: that rape is an abuse of power in sexual relationships; that rape is more widespread than people think; that almost all rape is perpetuated by men; and that 80% of raped women know their rapists, so it's unlikely that you can tell which men are dangerous and which are safe.
Also like other rhetoric, it's intended to grab an audience's attention. Some listeners will be outraged, some will be hooked, some will think it's ridiculous... In a world where 18 year olds will all (almost without exception) have been exposed to images and descriptions of graphic violence, heads exploding, war, casual images of death, political scheming, global exploitation, sex scenes, and indeed probably scenes of rape, it seems a little odd to want to protect them from ideas - especially ones as obviously simplistic as this one...