Regan —

Then let them anatomize Regan

Regan is usually considered more contemptible than Goneril. Her mind seems of a courser grain because her taunts like 'let him smell his way to Dover' are more appropriate to a butchery than a palace. Regan also seems the more vile because of her participation in the blinding of Gloster, although tearing out the old Earl's eyes was Goneril's suggestion.

REGAN
Hang him instantly.
GONERIL
Pluck out his eyes.

Despite the horror of the act, it needs to be understood from the perspective of Regan and Cornwall, who are as one in this matter. Gloster's motives are undoubtedly noble in that he wants to help Lear to Dover and safety with Cordelia. But he has also made contact with the French invaders and intends to join forces with them. This is an act of treason against the British party, and specifically against the Duchy of Cornwall in which the Earldom of Gloster exists. A traitor is usually thought of as an evil-doer because he performs his crime against the state. But if he performs his treason against an evil state he is reckoned as a good man. In either case, though, if he is caught he will suffer a terrible punishment because treason has always been regarded as a crime far worse than murder. Accordingly, Gloster suffers a horrid, but what Regan and Cornwall would regard as justifiable, punishment for a crime against their state. Cornwall makes it quite clear to Edmund that because a traitor must suffer a terrible punishment, he is 'bound' to inflict it on his father. It is almost as though he is saying to Edmund, "Sorry, I know he is your father and i would like to spare you the anguish, but the penalty has to fit the seriousness of the crime he has perpetrated. In consideration of your feelings I ask that you not be here to witness what must be done because they are not fit for your beholding."

Cornwall and Regan repeatedly describe Gloster as a traitor

EDMUND
This is the letter he spoke of, which approves him
an intelligent party to the advantages of France:
O heavens! that this treason were not, or not I the detector!

CORNWALL
Edmund, ..... the revenges we are bound
to take upon your traitorous father are
not fit for your beholding.
..... Go seek the traitor Gloster
..... Who's there? the traitor?
Enter GLOSTER, brought in

CORNWALL
Bind him, I say.
Servants bind him
REGAN
Hard, hard. O filthy traitor!
CORNWALL
To this chair bind him.
Regan plucks his beard
GLOSTER
By the kind gods, 'tis most ignobly done
To pluck me by the beard.
REGAN
So white, and such a traitor!
CORNWALL
And what confederacy have you with the traitors
Late footed in the kingdom?

REGAN
[urges Cornwall to blind Gloster - (as Goneril suggested)]
One side will mock another; the other too.

Out, treacherous villain!
Thou call'st on him that hates thee: it was he
That made the overture of thy treasons to us;

[and with ferocious sarcasm]
Go thrust him out at gates, and let him smell
His way to Dover.

As horrible as Gloster's blinding is, Regan would regard the punishment as legal and she kills the servant for his interference in Cornwall's administering of justice. Note that the messenger who tells Albany of Gloster's blinding refers to it as a punishment.

Messenger
Ay, my good lord; 'twas he [Edmund] inform'd against him;
And quit the house on purpose, that their punishment
Might have the freer course.

Later, when Regan offers Oswald 'preferment' she does so to correct her error, as she perceived it, of not having executed Gloster.

REGAN
It was great ignorance, Gloster's eyes being out,
To let him live:

If you do chance to hear of that blind traitor,
Preferment falls on him that cuts him off.

When Oswald meets Gloster and Edgar, he describes Gloster not only as a traitor but as a 'publish'd' traitor, so their seems little doubt that Gloster acts were regarded as crimes against the state.

OSWALD
A proclaim'd prize! Most happy!
That eyeless head of thine was first framed flesh
To raise my fortunes. Thou old unhappy traitor,
EDGAR interposes
OSWALD
Wherefore, bold peasant,
Darest thou support a publish'd traitor?

Goneril's influence reverbs a hollowness in Regan

Regan never questions, doubts or checks what Goneril tells her. Because Goneril's 'let's hit together' gains Regan's compliance against Lear, Goneril is able to manipulate Regan with exaggerations about Lear and his knights. Regan has not seen Lear since the division of the kingdom but Goneril's opinion and influence from that time still persists. There is nothing to justify Regan's neglect of Lear or her siding with Goneril. She has not one scrap of evidence against Lear.

GONERIL
If he dislike it, let him to our sister,
Whose mind and mine, I know, in that are one,

Goneril orders Oswald to write letters to Regan about her 'fears' and then add his own verbal account. Her fears are groundless, but she is obsessively determined to degrade Lear.

GONERIL
How now, Oswald!
What, have you writ that letter to my sister?
OSWALD
Yes, madam.
GONERIL
Inform her full of my particular fear;
And thereto add such reasons of your own
As may compact it more.

Not surprisingly, the dissatisfactions that Goneril expresses through Oswald are able to hoodwink Regan and Cornwall. They know nothing of the knights, good or bad, only what they are told. With no justification whatsoever, they immediately describe Lear's followers as riotous. They are further mislead when Edmund lies that Edgar associates with Lear's knights. Oswald adds his lies about Kent, who with sarcastic effrontery insults everyone. Cornwall forms an unfavorable opinion of Kent's behavior which he then quite unfairly, though understandably, attaches to Lear's knights: 'This is a fellow of the self-same colour our sister speaks of.' Little wonder that Regan and Cornwall think Goneril to be right and Lear to be wrong and his knights to be riotous. They are completely taken in!

GONERIL
. . . . . I have writ my sister
If she sustain him and his hundred knights
When I have show'd the unfitness,—

REGAN [about Edgar]
Was he not companion with the riotous knights
That tend upon my father?
GLOSTER
I know not, madam:
EDMUND [lying]
Yes, madam, he was of that consort.
REGAN
No marvel, then, though he were ill affected:
. . . . . I have this present evening from my sister
Been well inform'd of them; and with such cautions,

CORNWALL [about Kent]
This is a fellow of the self-same colour
Our sister speaks of. Come, bring away the stocks!

REGAN [to Lear]
She [Goneril] have restrain'd the riots of your followers,
. . . . . Dismissing half your train, come then to me:

REGAN
. . . . . Shut up your doors:
He is attended with a desperate train;
And what they may incense him to, being apt
To have his ear abused, wisdom bids fear.
CORNWALL
Shut up your doors, my lord; 'tis a wild night:
My Regan counsels well;