I thank CON for accepting this debate.
Argument 1: Plea Bargains and Capital Punishment
Plea deals in the United States are commonly used in most capital murder cases - almost up to 90% in the state of Virginia. [1 - p. 878]
Prosecutors will often bluff and use the threat of capital punishment to coerce innocent people to plea guilty to a crime they did not commit in order to avoid being executed. [2 - p. 172]
If capital punishment was banned, there would no longer be such an extreme threat to use to force people to gamble their lives on a trial.
It is also the case that depending on a location within a state depends on how likely you are to be offered a plea bargain and ultimately if the end outcome is state execution. Scholars have labelled the process "not grounded in fairness". [1 - p. 890]
If a system allows for the threat of death causes more cases of miscarriages of justice, if capital punishment in the United States was banned, the entire criminal justice system would be more just. Although this problem is inherent in all cases of plea bargain, the extent to which death places pressure on a defendant is unique.
Argument 2: Innocent People Executed
In the United States, since 1973, 167 people have been executed then subsequently exonerated, with Florida alone being responsible for 29 of these cases. 
In 2014, a study was done that found around 4% of people sat on death row are innocent and that it is almost certain more people will be executed when they have not done as alleged. 
All other forms of criminal punishments can be reversed if found to be innocent and even compensation can be given to the aggrieved party, but there is no way to compensate the deceased directly nor give justice to them.
Argument 3: Botched Executions
In a 2012 study of 9,000 U.S. executions, researchers found 270 executions had been botched. 
This is far too often to be ignored - particularly
To exemplify how dreadful these botched executions can be, the case of Jesse Joseph Tafero is a prime example. He was convicted in Florida of first-degree murder, armed robbery and rape and was subsequently executed by electrocution. The machine malfunctioned causing six-inch flames to shoot out of Tafero's head. It took 7 minutes for him to finally die as he was slowly burnt from the inside out. 
This is inhumane and against the ideals of the United States as laid out in the Constitution granting people freedom from cruel and inhumane punishments. Unless a solution can be given to this issue, the death penalty should be banned.
Argument 4: Punishments Must Fit the Crime
The decision of who is given the death penalty is too arbitrary to be just.
The case of Daniel Lewis Lee and Chevie Kehoe who were convicted of murdering a couple and their child exemplify this issue. Although most accounts show Kehoe instigated the violence, only Lee was sentenced to death. 
Justice is only legitimate if it is fair and the criteria for who is to be put to death is clearly defined. In the United States this is not the case. Unless a solution can be given to this issue, the death penalty should be banned.
Argument 5: Racism
"In 1990, the U.S. General Accounting Office reviewed numerous studies of patterns of racial discrimination
in death penalty sentencing. Their review found that for homicides committed under otherwise similar
circumstances, and where defendants had similar criminal histories, a defendant was several times more
likely to receive the death penalty if his victim were white than if his victim were African American". 
There are also issues with systemic racism. As Professor Vivian Miller reaffirms in a 2020 podcast on the issue, “It’s much more likely that a black defendant with a white victim will end up with an execution.” 
This leaves the death penalty as executing someone for their race, not on the basis of the crime. Unless a solution can be given to this issue, the death penalty should be banned.
Argument 6: Cost
The costs can be astronomical to perform capital punishment:
- "In Maryland death penalty cases cost 3 times more than non-death penalty cases, or $3 million for a single case".  
- "In California the current system costs $137 million per year; it would cost $11.5 million for a system without the death penalty". 
- "A Susquehanna University report found that, on average, across all 50 states, a death row inmate costs $1.12 million more than a general population inmate". 
Not only could this money be spent helping victims of crime or investing in crime prevention methods, there is no additional benefit to execution over life imprisonment.
My method in this argument is to point out fundamental flaws in the system that are so fundamental, capital punishment should be banned in the United States of America.