Lincoln's EP wasn't popular in the North or with Union soldiers for the reasons you outline, but as it began furthering the War effort, as outlined by Lee in his letter to Hunter, it gained support rapidly.
As for property rights, conservatives today constantly use the phrase "higher law", that their particular view of God's intent should trump any government written law or court ruling. By that standard, applied retro-actively, the US Constitution had no legitimate right to ever have declared any human beings as property.
It was a false provision that held no standing under theory of Creator-endowed right to liberty, much as today's conservatives argue about the Creator-endowed right to life. Change your Gore Decree to a Palin Decree let's say, one ending abortion with a penstroke, and I think you'd get a completely different reaction from those who would call such unilateral use of presidential power to be dangerous or an abuse.
I think we all recognize today, as did most folks in the 19th century finally realize, that the God-given rights of life, liberty and happiness trumped the US Constitution when it came to the natural human rights of the "property" in question, even though the path out was done constitutionally.
Even now I find it just repugnant to refer to the slaves as mere property, but Lincoln's careful and limited use of the EP was designed and implemented as a war tactic, not a high handed property grab.