Maybe this is obvious but I don't see it mentioned anywhere: everybody cares very little about transactions from people they're not involved with paying other people they know nothing about, it's just spam from the perspective of people not involved.

Also some random message written in an OP_RETURN is still more valuable (for anyone) than, for example, a financial transaction between two objectively evil people, for example, or, say, from mortal enemies of whoever is judging. In this sense a normal transaction can be worse than mere spam.

All of that considered, even your own transactions are still spam after they have been acknowledged as received then spent. At that point they're not even valuable to you anymore.

The entire blockchain history is spam.