Both Tamora and Titus are on missions of revenge. Aaron, on the other hand, despite his claims to the contrary, is not out for revenge. He is simply a villain, a role in which he takes the utmost pride and joy.
Tamora’s entire raison d’etre is revenge. Titus denies her pleas to save her son Alarbus from sacrifice, and Demetrius, another son, invokes revenge of mythic proportions:
Then, madam, stand resolv’d; but hope withal
The self-same gods, that arm’d the Queen of Troy
With opportunity of sharp revenge
Upon the Thracian tyrant in his tent,
May favour Tamora, the Queen of Goths
(When Goths were Goths, and Tamora was queen)
To quit the bloody wrongs upon her foes.
And she makes no effort to hide her motivation. Even to Saturninus, only moments after becoming his empress, Tamora reveals her goal concerning the Andronici:
I’ll find a day to massacre them all,
And raze their faction and their family,
The cruel father, and his traitorous sons,
To whom I sued for my dear son’s life;
And make them know what ’tis to let a queen
Kneel in the streets and beg for grace in vain.
Here, we see not only her objective (kill them all), but why: the failure of her suit to save the life of Alarbus. It is bad enough for her to lose her son; what’s worse is having to beg for his life in the first place. Having heard the power of her entreaty to Titus, we can certainly understand her desire, even if we cannot condone it. Her mission is clear, but things get messy, as they always do, in the actual execution (so to speak). It is not enough to attack Titus, she wants his sons to take the blame for her own sons’ murder of Bassianus. One might be able to accept that level of revenge, but the rape and mutilation of Lavinia goes far too far. Lavinia pleads for her life to Tamora, but the Goth Queen will hear none of it:
Hadst thou in person ne’er offended me,
Even for (Titus') sake am I pitiless.
Remember, boys, I pour’d forth tears in vain
To save your brother from the sacrifice;
But fierce Andronicus would not relent:
Therefore, away with her, and use her as you will:
The worse to her, the better lov’d of me.
Again, we see the root cause of her vengeance, the loss of her son. But then, unbelievably, she tells her sons to rape Lavinia, not only for their enjoyment (“use her as you will”), but FOR her, their mother’s, fulfillment as well (“the worse to her, the better lov’d of me”). It’s wicked, scary stuff.
The result of this act of revenge is, however, simply more revenge: as Titus looks on his mutilated, speechless daughter, he plots,
Let us, that have our tongues,
Plot some device of further misery,
To make us wonder’d at in time to come.
Revenge will be the device of “further misery,” a revenge of such spectacular extremes that we as readers, centuries removed, “wonder” at its barbarity… and that’s BEFORE he loses his hand and Martius and Quintus lose their heads. After that, any hope for restraint or even resignation are gone:
For these two heads do seem to speak to me,
And threat me I shall never come to bliss
Till all these mischiefs be return’d again
Even in their throats that have committed them.
He doesn’t know who will be the object of his revenge yet, but there’s a nice little piece of foreshadowing, all the same: “throats” WILL be cut.
The whole philosophical/aesthetic concept of revenge, one that both Seneca and Thomas Kyd understood centuries ago and that Mel Gibson has absorbed today, is that if revenge is warranted, of the precipitating wrong is heinous enough, then the audience will go along. And we do go along. Titus is our main character, a man of war, a man of principles (not necessarily ones to which we ourselves subscribe, but principled all the same), and when he suffers his loss, no matter if they stem from his own decision, we understand the inequity of it all, and can (possibly) support his attempt at retribution. Tamora, too, earns our support through an exceedingly well-argued appeal to save her son; when that appeal falls on Titus’ deaf ears, we, here as well, understand and (again possibly) support her attempt at vengeance (until it goes too far).
What we cannot, at any level, support (or even understand) is villainy. And that is the realm in which Aaron works his charms. He can, and does–with glee–list his villainies (over which his only regret is having “not done a thousand more” (V.i.124). But he does not (because he cannot) call any of these revenge. He knows the limitlessness of others’ revenge (“without controlment, justice” [II.i.68]), and doesn’t want to tempt the consequences. He knows that to cross these bounds is to simply “plot your deaths // By this device” (II.i.78-79).
He can threaten a “vengeance (to) rot you all” (V.i.58), but it’s only a tool, a negotiation tactic to save his son. He understands the power of revenge, but he doesn’t have that power, that need… he has only villainy. Aaron may tell Tamora that “Vengeance is in (his) heart, death in (his) hand, // Blood and revenge are hammering in (his) head” (II.iii.38-39), but even here, he cannot convincingly state that he is doing anything in the name of vengeance; in this context, “hammering” not only refers to beating, but also to arguing, debating: bloodlust and revenge are arguing with each other in Aaron’s brain. But it is blood that Aaron truly wants, because — quite simply — he has no cause nor need for revenge.
It’s interesting to note that Aaron is the only character in the play to have true soliloquies (in II.i, II.iii, and IV.ii; Lucius has what could be considered to be a soliloquy at the end of Act Three, Scene One… however, this could be spoken to his family before they exit, or to young Lucius [as in the Taymor adaptation]); he speaks to us, and even in these moments, he cannot convince us of his need for vengeance. In fact, he doesn’t even try… because he has no cause. Aaron is simply a character of bad deeds, a cypher/symbol who says in his final words of the play, “If one good deed in all my life I did, // I do repent it from my very soul” (V.iii.189-190). It’s a laughable send-off. Aaron has no soul, no soul to be so wronged as to warrant revenge.
If Vengeance is the repayment of a god, then both Tamora and Titus “draw near the nature of the gods” (I.i.120), though not “in being merciful” (I.i.121), but in being UNmerciful. Tamora and Titus may have vengeful near-apotheoses, but Aaron, in the end, isn’t even a man, but a self-proclaimed “devil” (V.i.147), who deserves not revenge, but retribution.