The Constitution ducked the issue and it ended up costing us 600,000 lives to fix the problem
I disagree. It didn't duck the issue, it couldn't resolve the issue. With the overwhelming majority of America involved either directly or indirectly in some way with agriculture/slavery, do you think the Constitution would have ever been ratified if it banned slavery?
Now, they DID ban slave trade. You could no longer go down to Charleston and buy a slave fresh off the boat. That ended with the Constitution. This is fairly significant given the importance of slaves to the plantations at the time. The fact they did accomplish this much is a complete refutation of the argument they ducked the issue.
In addition, they worded the Constitution and preamble so that it became a righteous sword for future abolitionists. They knew that the day would come when the people would be ready to end slavery and liberate those in shackles. They gave them the tools to do that when the time came.
Of course, when that time came, justices on the courts ruled slaves were property. It was upon that ruling we had a splitting of opinions across America and suddenly, abolition became a social issue versus a state's rights issue. This is what prompted the war. It was the failure of the courts and congress to find a resolution.