Well, I don't think it's a good analogy in a few ways. It's probably closer to a restraining order than a breakup, even though that analogy isn't perfect either.
And there's a significant power imbalance between large and small accounts. A small account blocking a large account doesn't impart any noticeable second order effects on the large account. But a large account blocking a small account absolutely can impart negative second order effects on the small account.
(And large accounts can certainly develop a sense of self importance or arrogance that leads to liberal blocking behavior)
The problem is that it isn't just two accounts interacting. The blocker may interact with someone else you follow, or who follows you, which then elides context from conversations.
Hypothetical:
Let's say John Carmack starts a discussion about Voxel Octrees, and Jonathan Blow comments on that. And Carmack comments back, and this goes on once or twice. You also have something to say on Voxel Octrees, maybe you're working with them in your project, so you want to join the conversation.
Unfortunately, Jonathan Blow has blocked you. You don't have any desire to interact with him. You would comment on Voxel Octrees even if Blow wasn't involved. But he has inserted himself into a conversation that you want to be a part of so now parts of that conversation are missing to you, and you have to log into an alt to get the full context of what is being discussed.
Hiding the blocker's posts from the blockee doesn't just damage the ability of the blockee to interact with the blocker, but also to interact with accounts that the blocker interacts with... and accounts that interact with that interaction, and so on.
That's clearly damaging the blockee's user experience. And there's a contingent of pro-block users who want to make the block even more repressive, such as hiding content with an IP ban.