By allowing all users the ability to create a stamp, you're allowing them to set any field to any value they want. Yes there are permissions you can lock down on fields, but if it's a field they normally can change, for example a Status field, they're no longer limited to select list options. They could mark an invoice "Approved" for example when they're not supposed to, potentially kicking off workflows, etc. This is a loophole that needs to be closed. Simply putting back Stamp creation in the functional profile would fix this.