I favor a breakup. Generally I have viewed Facebook and Instagram as honeypots which attract people who otherwise would just involve themselves in other equally damaging addictive activities. In that sense, they wouldn’t really affect the lives of those who choose not to use them.
The problem arises when those who are addicted to the services get to vote in elections. At that point, the damage escapes the honeypot and can influence others in meaningful ways.
Breaking them up helps solve this by preventing any one company from essentially taking over the world’s democracies by steering allowable debate and therefore votes. It also distributes the attack surface area for other countries who want to influence elections.
I absolutely believe undoing the Instagram merger and stopping Facebook from copying the features of other networks to kill them would help accomplish this objective.