How to let give up to use 'shutdown abort'

Hello everyone,

# Sorry, I’m not well English.

I have a worry. I’d like you to give me opinions about below.

“Shutdown abort” is known as unsafely command to stop database.

But my customer persist that should use this command to complete failover as quick as possible.

I think safety is more important than time for database.

I dissuaded him, but he don’t accept yet.

He persist  “There is no matter to use 'shutdown abort’. because oracle database has instance recovery mechanism. so oracle database can startup even if server downed abnormally."

To persuade him, I need to find critical problems related to use 'shutdown abort’.