I don't get your argument. It seems that you're saying that if something can't be made 100% secure, then there is no point trying to make it more secure than it already is.
Im saying, as things get more secure you can start to move your information there (as i said with email, dropbox or your own servers). Use the online medium that matches your documents safety requirements.
If your a security guru then out of all those your own servers that you harden yourself would probably be the most secure. For non security guru's maybe email or dropbox do a better job.
No one ever said dont make it more secure, but as the sophistication of the security methods goes up over time so will the sophistication of the crackers/hackers. This means your judgement not matter how much better security gets will always play a apart.
Im stating that you shouldnt rely on others for security. Whether dropbox, or a clone. Stating that dropbox as a vendor cant be trusted isnt a valid as it will apply to all the clones. Bottom line you should take responsibility of your own files. Any new system that tries to be more secure will "most probably" still have security issues with it anyway.