1. There is already a lot of administrative bloat in the academia, and ideas like this are responsible for most of it. Every time you replace an informal process with a formal one, you add to the bloat. And the formal process rarely works as intended.
2. Letter-writers have no control over the work of the person they recommend. They cannot prevent the submission of a manuscript or a grant. They would be taking a lot of risk for no gain.
3. Letters of recommendation are a form of corruption and nepotism. If you would have a conflict of interest for reviewing a manuscript or a grant, you should not be allowed to write a letter of recommendation either.
2. Letter-writers have no control over the work of the person they recommend. They cannot prevent the submission of a manuscript or a grant. They would be taking a lot of risk for no gain.
3. Letters of recommendation are a form of corruption and nepotism. If you would have a conflict of interest for reviewing a manuscript or a grant, you should not be allowed to write a letter of recommendation either.