I think this is a thin and biased definition of mercy expressed in the OP. The universalist doesn't define mercy as something "not deserved" but something beyond desert, because love is beyond desert. You don't love someone because you owe them something; you love them because you do. In this sense, God's mercy is actually the end of, and a form of escape to, His punishing sin in this life, for men are rewarded according to their work in this life (Psalm 62:12), which brings me to the next point: the concept of death and sin, to the universalist, is not something that should even be considered post-mortem. Indeed, imitating Jesus, it isn't necessary to worry for tomorrow, for tomorrow will have its own troubles. The concepts of sin and death have refernce to now (cf. Romans 7), unambiguously, and consequently salvation has reference to now, as indicated by Matthew 1:21 for instance, that states that Christ has come to save men from their sins, and the prayer of Christ in John 17:3 that declares that eternal life is now, something qualitative, not quantitative. The universalist isn't saying that everyone will get a "free ride" in regards to heaven; he is saying that sin is very much a difficulty and problem and punishment overlooked by many a myopic theologian. Cf. Calvinist theologian Erwin Lutzer, who stated that if all men will be redeemed after death, there is therefore no "pressing need" to preach the gospel. Nonsense. The gospel is life and life in abundance -- now. The soul is condemned, hence the soul needs an easy yoke. These concepts are littered all throughout the New Testament. We perish not because there is a Hell after death, but because our souls have died; accepting Christ the paramount means by which we are given new life.
Mercy is simply that form of benevolence expressed from a higher power to a lower -- in this case, from God to man. To say that it is "not getting what you want" is not necessarily so, and is also dangerous to your conception of justice. By upholding this form of mercy you are simultaneously contradicting the justice that is so very essential to benevolence; for it is in giving men what they don't deserve that you are breaking what they do. The universalist says, echoing George MacDonald and the psalmist in Psalm 62:12, that there is no dichotomy between mercy and justice; that in God mercy and justice meet; that without justice to the full there can be no mercy, and without mercy to the full there can be no justice.