Sure, if you wait for a sufficiently large weight on top of your transaction, then you solve the double spend problem. But you need at the bare minimum that every transaction that happened at roughly the same time as yours to be included as an indirect child of your tips. If you do not understand that sentence, please try to, as it is the very reason that IOTA doesn't scale (and isn't fundamentally different from usual blockchains in any sense other than a somewhat contrived construction).