So they left because they thought Lincoln would interfere with their right to own slaves. Where in the Constitution is slavery a “protected right”
Article I, Section 2, Clause 3; Article I, Section 9, Clause 1; and Article V contain wording that provides sanctions for slavery.
If you are going to argue this issue, you need to catch yourself up.
No Person held to Service or Labour in one State, under the Laws thereof, escaping into another, shall, in Consequence of any Law or Regulation therein, be discharged from such Service or Labour, but shall be delivered up on Claim of the Party to whom such Service or Labour may be due.
Though the word "slave" isn't mentioned in the US Constitution, that clause was put in there specifically to guarantee the return of slaves fleeing their masters.
It makes it virtually impossible to create a "free" state, and indeed, George Washington himself kept slaves in Pennsylvania after it had become a "free" state by simply rotating them in and out from his other plantations in other states.
Since the "free" states were constitutionally obligated to recognize the property rights of slave owners, how are you going to keep slave owners from coming into your state?
They had a right to do that under the US Constitution.
No, the problem was baked into the cake from the very beginning.