My mistake, I meant the opposite: electrolytic corrosion. There are potential (non-electrical) chemical variables too. The chemistry involved is complicated and I can’t claim to fully understand it. Even big automakers sometimes get it wrong from the factory.

It's more likely they used plastic simply because they could mould the whole thing.

I am sure that is the case. I was never suggesting that this part was intentionally chosen to be plastic because nothing else could work. There’s hundreds of materials you can make a fitting out of, and likely dozens of materials would work, with varying pros and cons. I’m saying this is typically a problem that would have a carefully engineered solution.

All this says to me is that you don't have any experience fixing plumbing, HVAC, or anything related. This whole line of reason has been completely ridiculous, and you ought to just stop.

I think you are reading too deeply into my comments, and thinking I am arguing something I am not.