Also, in case of the amount, the user can verify it, because it's human-readable.
Aliases r readable too.
Problem is aliases need to be looked up, and you have to be sure no one is poisoning the alias lookup with fake info (associated id). So you have to do at least 5+ lookups from different peers to be sure that the ID is correct.. (Is this correct?) - That's not very fast and you won't reach 10,000 tps (or however many you want) this way. I may be wrong.
Future clients will sign transactions by themselves. Sending a secret phrase to a remote node is insecure. That's why input should be validated on client side.