The Paris Agreement is useful in creating goals for emission targets so countries can work towards them. Sure, the goal posts can and will change, but they'll always be pointed downfield.

If the US creates an alternative to the Paris Agreement that has more teeth, there might be an opportunity cost. Until then, this is the best thing we have.

How about just take part, and not pretend?

The message being sent here is, "in the global coordination problem of climate change, I'm the defector and the freeloader, and I need to be coerced to take part".