If you’re not convinced yet that writing to dual masters is a bad idea, we have a couple more reasons.
9. Temp tables break replication after restart
MySQL’s replication is sensitive to temporary tables. You shouldn’t use them. If your queries create them to work against, and a node crashes, the temp tables will be missing upon restart. You can imagine what this will do to all those queries which expect to see a temp table. That’s right, they’ll fail.
Theoretically you could have a start script which creates and populates such temp tables. However this may add operational complexity if not carefully coordinated with developers & change management.