This functionality is there because it allows contracts to interact with each other. This allows a million different type of applications, e.g you could create a crowdfund using a gold token hold by a multisgn.

The contracts are usually trusted and their addresses set from beginning, so this is never an issue (unlike what the article implies). The DAO however allowed an arbitrary address to be used as the contract to talk to. This is flexible because it allows contracts to be update themselves, or update who they talk to, but if the contract is malicious and there is a reentrancy, then that's the issue, but again, it's the contracts fault, not the whole platform.