Stealing people's coins is a red line

UTXOs are sacred. We don't fork to steal them. We don't fork to expire them. We don't fork cancel them.

This is the slippery slope.

This is the hill worth dying on.

Did BIP 16 makes some coins unspendable?

The BIP turned a particular "hashlock" locking script pattern (OP_HASH160 OP_DATA_20 20-byte-value OP_EQUAL) into a "magical" bytecode pattern which, after authenticating an input's top stack element against the hash then also executes it using Script VM.

The BIP references 1 historical transaction that spent from an output that matched the pattern:

These new rules should only be applied when validating transactions in blocks with timestamps >= 1333238400 (Apr 1 2012) [1]. There are transactions earlier than 1333238400 in the block chain that fail these new validation rules. [2]. Older transactions must be validated under the old rules. (see the Backwards Compatibility section for details).

which made me wonder - are there other, unspent, historical hashlock outputs which may have been made unspendable (if they weren't already) by introduction of the P2SH feature?

Even before BIP-0016 activation, there were some outputs that matched the P2SH pattern. Only one of them was spent before activation, and the rest have likely been made unspendable by the BIP-0016 upgrade since spending them would have to satisfy consensus rules not enforced when they were created. Total amount locked in those outputs was 0.044 BTC.

Before P2SH activation, they could be spent as just hashlock contracts. After P2SH activation, they could only be spent if the hash preimage also happened to be a redeem script that would pass execution.

The TXO created in block 170052 was actually spent in block 170060 as hashlock, not P2SH, because P2SH rules weren't active at the time.

So was it a mistake or was it intentional?

    // BIP16 didn't become active until Apr 1 2012 (on mainnet, and
    // retroactively applied to testnet)
    // However, only one historical block violated the P2SH rules (on both
    // mainnet and testnet).
    // Similarly, only one historical block violated the TAPROOT rules on
    // mainnet.
    // For simplicity, always leave P2SH+WITNESS+TAPROOT on except for the two
    // violating blocks.

Intention doesn't even matter: if you run anything greater than Core v 0.6.0, you are actively preventing five utxos from being spent

For those wondering how this relates to the spam debate, some people on the Core side like to say they oppose any attempts to disable the utxos of spammers because confiscation is unconscionable. But their node is actively keeping old utxos unspendable too

If the best counter you've got is "it happened 13 years ago and there's a chance it was by accident" then I'll remind you that the confiscatory rule is still in your node right now. You can eliminate it if confiscation violates your principles. You can't claim ignorance.

The nuances

There is a major difference, the outputs made unspendable by P2SH were anyone-can-spend before (i.e. weren't secured by a signature) and so had no ownership guarantees to begin with. Also we're talking about 0.044 BTC at 2012 prices, less than a single dollar.

If you think it's okay to maintain that confiscatory rule to avoid bad consequences, maybe show a little grace toward those who want to add a new confiscatory rule to eliminate different bad consequences.