If everyone bought from Temu then the net benefit would be zero relative to just including it in the price right?

In practice the value flows from people who don't buy cheap crap from China to people who do.

This amounts to a subsidy of Chinese manufacturing over local manufacturing.

I can’t see how a market distortion is a net benefit to the importing country.

It seems self-destructive.

One might even refer to it as a "public service".

It’s a classic negative externality. Not every taxpayer partakes in this pathological consumerism.