But it seems as if some core developers have ulterior motives?
Yes. To stop being responsible for the on-chain content at all:
https://bitcoincore.org/en/2025/06/06/relay-statement/Why else would they want to push through with making an exploitable bitcoin feature official instead of completely removing it?
Because "completely removing it" would mean using things like standardness rules, to block these things. And then, miners would start confirming all non-standard transactions, blocking all of the upgradeability, which is possible, as long as most users stick with standard transactions.
They will unfairly use their position to push the Lightning Network until someone stops them.
Yes, the main on-chain network will be expensive to use in the future. Which means, that if you will want to have a single UTXO per user, then it will cost you a lot of satoshis. And it is by design, because if you have small blocks, then you have high fees, to make an incentive to mine next blocks, where halvings will bring down the basic block reward to zero.
In the future, regular people will move coins only on second layers. They may never see their coins on-chain, but only observe, that their data are committed to some UTXO, shared by a lot of other users.
If you want on-chain scaling, then BTC is not going in that direction. Soon, you will be forced to use altcoins, if you believe in on-chain scaling. Or: if you want to see any blockchain, then you will be forced to use sidechains (but it is kind of second layer, so coins are at least pegged into real BTCs; also, after being confirmed on the mainchain, sidechains can be pruned, so they don't have to use constantly growing chain during their Initial Blockchain Download; only mainnet has this problem, because there is no upper layer to commit to).
It is a policy change, not a consensus change. How stupid is everyone in this thread?
Yeah, people think, that allowing spammy transactions means endorsing them. But it is not the case. Instead, it is like a honeypot, because if spammers will use currently known methods to spam, then it can be easily ignored by future versions. Next limits will be lifted, so that developers will no longer be responsible for on-chain content. And also, by lifting these limits, it will block any ideas of increasing the maximum block size, because if someone will try doing it, then that person will be flooded by a lot of non-monetary transactions. Now, there are images, if block size will be increased, then we will have videos.
if they turn Bitcoin into Ethereum, it would be the end of Bitcoin
Why? On top of any spammy network, you can make a subnetwork, which would have much stricter rules. And then, people willing to use blockchain to transact, will still have their well-optimized nodes, while leaving the whole crowd of spammers unaffected. If people want to waste a lot of resources for storing JPEGs, it is their choice. More filtered networks will grow in value, if users will compain about no longer being able to meet minimal requirements to run nodes. And then, they will switch to subnetworks, which allows only monetary transactions, instead of allowing everything.