If security is your concern, then the best option is to display a warning. You do the same for .exe files.

If spam is your concern, then excising the feature doesn't stop the spam. Users are already spammed by fake files, mislabeled results, etc., and I'm sure other spamming opportunities exist. Excising the html launch feature does not preclude spammers from sending bogus results.

It may be that you really have other, less virtuous concerns and that is why you want to excise the feature. I'm not sure such concerns will stand up in the face of public scrutiny though. They'll probably be viewed as anti-competitive and monopolistic, and at least adverse to your open protocol and networks mantra.