So if I'm understanding things, folks in favor of removing OP_RETURN are worried about mining centralization because sneaky transactions are already happening and this will cause mining centralization. On the other side, folks in favor of keeping OP_RETURN are worried about storage of child porn and non-financial data. Do I have that right?

In the link you posted, the author stats that non-financial data will eventually get priced out of being on bitcoin. If that's true, then isn't the centralization of miners a temporary issue, as well?

Let's say that miners become centralized for a period of time. But then eventually bitcoin mining fees rip and non-financial data becomes untenable. At that point wouldn't miners start to decentralize? Or is the thought that once miners centralize it's the point of no return and/or that bitcoin fails?