SP2013: Calling SP.ClientContext for an anonymous user causes "object doesnt support this method"

Good Morning!, and what a wonderful Saturday morning it is, the scent of strawberries are in the air!

So I've been working on a public facing 365 website lately and making a few customisations, one request I received was to have the ability for users to add an item to a "mailing list" list, and they wanted maximum portability, so I thought, perfect for the JS-CSOM!

Such a simple idea, add an item to a list, just needs one field adding in very straight forward, or so I thought, so I created the js function and hooked it up, for auth users it worked like a charm but I ran into a problem when accessing it anonymously, I got the error "object doesn't support this method" when calling a new "SP.ClientContext", its a straight forward error meaning it cant find the function in any loaded libraries, so I thought right, gotta be SP not loading sp.js, simple, add a script link in there... no luck the same error came up, then I thought right, gotta be that the method is running before SP.js is properly loaded so I used "ExecuteOrDelayUntilScriptLoaded()" to encapsulate my code and make sure it runs after the code is loaded, published the js and checked it again... no luck!

So it has to be sp.js not loading correctly, remembering the SoD SharePoint is so fond of I then tried the trusty "SP.SOD.executeFunc('sp.js', 'SP.ClientContext', addToMailingList)", and it worked perfectly!

Code:

$("#ben-mailinglist-confirm").click(function () {
    SP.SOD.executeFunc('sp.js', 'SP.ClientContext', addToMailingList)
});

function addToMailingList(metadata) {
    var metadata = $("#ben-mailinglist-email").val();
    if (metadata != "") {
        var clientContext = new SP.ClientContext("/");
        var list = clientContext.get_web().get_lists().getByTitle('MailingList');

        var itemCreateInfo = new SP.ListItemCreationInformation();
        var listItem = list.addItem(itemCreateInfo);
        listItem.set_item('Title', metadata);
        listItem.update();

        clientContext.load(listItem);
        clientContext.executeQueryAsync(
       Function.createDelegate(this, function () { $(".ben-mailinglist-success").show(); $(".ben-mailinglist-form").hide(); }),
       Function.createDelegate(this, function () { $(".ben-mailinglist-failure").show(); })
   );
    }
    else {
        // validation
    }
}