the constitution specifically bans slavery. it doesn't say that the federal government (let alone the courts) has the right to legislate and define the definition of marriage
the tenth amendment specifically delegates unmentioned and unprohibited rights to the states themselves
The constitution does not ban slavery. However, you are right, the 10th Amendment does subject marriage equality to the legislators at a state level. And a lot of states are dealing with that in their own ways. However, I don't think that inequality at any level of government should be tolerated for longer than it needs to be, and the fact that if same-love marriage was legalized at a federal not a single person in this country would be realistically harmed by that, means it probably just should be legal in the first place.
Only things that can cause harm should be illegal, don't you agree?