I think I get it now. So Blockchain.info's wallet use to have a field for adding custom messages via a public note field.
This was "potentially" creating lot of un-spendable outputs. Ie bloating the blockchain in a bad way.
"Yes, please don't create lots of unspendable scriptPubKeys. There are
more prunable ways of embedding messages into transactions. And there
are even better ways of associating messages with transactions, so
only people involved with the transaction can read the message (if
In other words, lets figure out how to do this the right way. The way
you're doing it now will stop working as soon as the network upgrades
anyway (0-value outputs are nonstandard as of the 0.7 release)."
When the OP_RETURN drama eventually passed, this allowed any kind of meta data to be stored on the blockchain to the tune of 80 bytes in a "friendlier" way.
Coloredcoin (and others) then made extensive use of this but because it uses the OP_RETURN code, this means that transactions are not stuck in limbo in UTXO and in addition, they can be removed or "pruned" with no detrimental effect.
In summary, adding non-bitcoin/ledger related data to the blockchain is only frowned upon by the people in the "use the bitcoin blockchain only for financial data" camp. With OP_RETURN, it is not such a big deal now because it can be pruned and keeps the people who want to put meta data on the blockchain happy.