Michael, there's no difference in "attractiveness" between what I'm saying and your description. The visual and navigation experience for a legitimate user is exactly the same: they submit the form and then the form disappears and they see the link to the content on the page "below" where the form was, without going to a new page.
While you can stop someone from properly closing the modal form ("modal" is when a form appears to be on top of everything else and usually sits on a grayed-out background) if the URL is always in the HTML "below" the form a mildly curious user can just copy the URL off your page regardless of whether they've submitted or X'd out of the form. In two seconds they can do View-Source or open Developer Tools and copy the URL. It's no real protection at all against someone who really wants your asset, and they don't have to be a "hacker" per se nor know how to code.
On the other hand, if you use the "Follow Up" URL -- this is exactly what it's designed for -- then the URL doesn't even exist in the HTML source until they've successfully submitted the form. So whether or not you disable the "X", they won't be able to grab your asset unless they have successfully filled out the form (whether their information is genuine is another question, but at least you have put the URL out of their reach until they fill in someone's email). A concerted hacker could avoid filling in an email address at all, though they might as well just use a@b.com, but you've made a good-faith attempt to make it harder for them. The challenge of finding View-Source doesn't rise to that level, IMO.
Do you see the difference?
Anyway, removing the "X" is as simple as MktoForms2 :: Lightbox :: Remove Close X
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