Why to spend time and efforts for adding useless generics in the first place? Maybe it would be better spending this time on performance optimizations, compile times optimizations and binary size optimizations instead.

Because I would rather write one generic container library than n slightly different ones for each data type of deal with screwing around with casting interfaces?

This sounds good in theory. What about practice? Could you provide a few links to popular Go packages, which benefit from using generics?

Because it's extremely useful to have adaptable data structures, without byzantine code generation?

Could you provide links to a few Go packages, which implement useful generic-based data structures?

Try google.

Because they’re not useless.

Thanks for very strong argument :)

No weaker than yours :)