As with many things, the key is moderation. Copper occurs naturally in the earth so you probably have it in your soil anyway, meaning it's not a contaminant unless you add such huge quantities the balance changes. It's also not a 'heavy' metal. You will be swallowing it anyway - whether you like it or not - and if you didn't, you would suffer health problems in much the same way you would if you had too much of it.
I agree with the issues of environmental pollution and the drive on that would be to improve mining practices since it will always be important to extract copper (it is used so widely in many industries - a great conductor, vital to many chemical reactions etc.).
If there were a better way to prevent peach leaf curl, I'd be happy to evaluate the alternatives but beyond keeping peach trees under cover, I'm not aware of one?