It won't destroy Steemit, it would help it growing past. We need bandwidth for the getting SMTs, follow is just one unworthy transaction which is wasting the network resources and if we could some stop that from happening the Steemit Network will be at advantage.
Maybe you are correct when you say there are people who just use Steemit on specific days and that would be a problem for them thou. I am just trying to put my little head to stop follow spamming on the network.