>Why should zoning laws be fought tooth-and-nail?
Because infringing on people's right to do what they want with their property deserves a hell of a lot more scrutiny than it gets right now. Trying to centrally manage what can be done where doesn't scale. See SF housing prices.
>Can I open a nightclub in my house?
As long as it meets the standards that night clubs have to meet then sure. You're unlikely to be able to do these things and be commercially successful enough to subsity in primarily residential area.
>What about parking? Can I pave my front lawn and rent the space out as parking spots? Or maybe put a dumpster there for local businesses to put their trash in?
Sure. Just be aware that you might be on the hook if you do a half-assed paving job and the runoff affects your neighbors. Once again if you truly are in a residential area where this kind of thing is not appropriate you will have a hard time being successful enough at it to annoy anyone who isn't already annoyed by everything.
>There's a tree on my boulevard. Can I cut the tree down and park a truck on the boulevard?
This is more complicated because you get into right of way issues and the city usually has a pretty substantial right of way beside the road (sidewalk?) but sure, if none of that is an issue then feel free to cut it down.
>I decided to run a grow-op in my house. When I turn the electricity on, the lights fade in my neighbours houses because the load on my grow-up is so much bigger than the equipment is designed to support.
If the power company was worried about QoS to the other customers on the street they wouldn't give you the massive breaker you need for that operation. If the neighbors are really bothered by it they can complain to the power company and if they complain enough then it will get addressed. There is no need for laws for this sort of thing. Once again if you're really in a residential area you're unlikely to get that kind of service if you really are somewhere it would be a problem. The power company has internal rules about what service gets installed where (basically their own zoning) in order to ensure that breakers on bigger equipment upstream are not tripped during times of peak load.