Allow me to ask, does God have the right to command the death of anyone? Clearly He does, since He commanded Israelites to kill all the Canaanites.
The reason God can make such a request is because no man deserves to live at all. Ezekiel 18:20 says, “The soul that sinneth, it shall die” and Paul tells us that “the wages of sin is death.” This being the case, because every person is a sinner, each person deserves to die, and every moment God suspends our death is due to His longsuffering and mercy. Thus, if He gives the command for anyone to die, it is well within the bounds of His justice.
It is the pure grace of God that He does not give the sinner what he deserves the moment he deserves it. So asking Abraham to kill Isaac was asking him to do what Isaac deserved. Let this be a reminder to you of how merciful God has been to you in not giving you what you deserve.