Lacking a secure drop off point is a service issue between you and the company delivering the package. It's just as possible to install a lock box or a set a pickup point or require a signed delivery. Complain to Amazon if they're too cheap to do anything about porch piracy. The convenience of opening your door for a package doesn't stand up to my right to privacy.
For the rest of your points: sure, if you really need a camera to watch your private porch then feel free to aim it at the porch and not the entire street. I'm not saying it should be illegal to monitor your property but that your right to 24/7 monitoring ends where your property line does.