In my opinion the problem is much deeper. Securities, by their definition, are contracts. In other words, they are agreements. They have consequences outside of the virtual domain. For securities to work there has to be some sanction for braking the contract.
Typical conditions for any security is that the management must inform investors honestly. Now, how on earth, we can get a distributed tribunal to judge that? What kind of sanction can be applied in a quasi anonymous habitat where nicks are dime per dozen?
Something like whoever makes a block with this transaction will be a judge does not work, because you need some qualifications to be a judge. For instance, judge should not be 12 year old. Please keep in mind that there is no restriction on age of miners.