Is there any security with suPHP?

I asked this question a while back and even though I put up several bounties, I never got much of an answer (see here). More generally, I want to know if there is any concept of security with suPHP? What's to stop anyone from going to

www.example.com/rm-f-r.php

www.example.com/return_some_iamge.php

Because those scripts get executed with the privileges of the user, it's essentially guaranteed acesss.

EDIT To elaborate on the above, my problem is a conceptual one. Assume we have a file at /home/user/test.php. Let this file do anything (rm -f -r /, fetch and return a picture, reboot the computer...) If I point my browser to that file (assuming the containing folder is an enabled site under Apache) how do I tell the browser to only let the owner of that file execute it?

EDIT 2: I never explicitly stated this as I assumed suPHP is only used with apache (ie. web browsers), but I am talking about authenticating linux users with only a browser. If we do not authenticate, then anyone technically has access to any script on the server (with web sites this is not a problem as they always have permissions set to 0644, so essentially the whole world can see. PHP files on the other hand, have permissions generally set to 0700)

suPHP has the effect that the PHP runtime executes with the permission of the user that authored the .php file. This means that a PHP program author can only read and write files that he himself owns, or otherwise has access to.

If you put a PHP file on your website you are making it publicly runnable by anyone that comes along to your website - using suPHP does not change this. Without logging in to your site, all web users are effectively anonymous and there is no way to reliably identify an individual. suPHP only controls the local permissions the script will have when it is executed, it does not intend to introduce any form of web user authentication or authorisation.

If you wish to control which users can actually run a script, you need to implement some login functionality and force the users to log in to your site. Then add a check to the sensitive PHP script (or Apache configuration) which will make it abort the request, if the current logged in web user is not one you wish to execute that script.