We all know that these additions to Bitcoin Core have slowed down transactions and made transactions more expensive.
Ordinals are not an addition to Bitcoin Core. People just take advantage of Bitcoin allowing arbitrary data being embedded in transactions.
It's just using the loophole that the Core team put in to give the Lightning Network a leg up. I wish people had the same energy for Ordinals that they have for Lightning, both are equally dumb.
What is the justification for them?
What kind of justification would be sufficient to you? They are valid transactions, and therefore are allowed by the protocol.
No justification is ever needed to anyone for using the blockchain.
Why are they being added when they make the network less efficient?
They don't make the network less efficient. They just increase the fees. That's expected to happen either way sooner or later to sustain the miners' income.
I think they do serve a good purpose. They show the developer bias and that Bitcoin is being run by a team of people who want to control what you use it for, while expecting other developers not to use the same tools to build that they do. This hypocrisy has gone to extreme levels. I see devs on social media bashing people for shilling shitcoins and then in their next post they're shilling liquid tokens or some other nonsense.