What if the goal is to regulate diesel out of existence unless it can be much better pollution-wise? What if the car companies could make a much cleaner diesel

What if the goal is to regulate diesel out of existence unless it can be much better pollution-wise? What if the car companies could make a much cleaner diesel engine, but it just wasn't cost efficient? What if this kind of regulation is the stick to go with the various green regulation carrots (tax credits on fuel efficient vehicles, subsidies for renewables, etc...)? What if making lawmakers responsible for legislating something out of business has unintended effects? Consider that in some places tobacco companies are suing governments over labeling, imagine the lawsuits if a car company could sue when they didn't like emission laws. I agree it is easy to look at this with a sympathetic eye to automakers, but I think we cannot condone cheating when other alternatives exists. It may well be impossible to build a clean enough diesel engine. If so we should drop diesel and figure out something with another energy store