Regarding emissions, it's a tradeoff: increased engine temperature increases NOx emissions, but also increases fuel economy, decreasing carbon emissions. I was unable to quickly find a consensus on which type of emission is worse or how to weigh one versus another.

Regarding regulatory compliance, defeat devices are clearly unacceptable; if the regulated requirements are considered inappropriate for whatever reason, they should be challenged through political or legal process, not by detecting test conditions and altering behavior.