While Mr. Deas at first seems on the side of order over truth (his telling Atticus that he has “everything to lose” from defending Tom brings out Atticus’s notoriously dangerous response, “Do you really think so?” [15.20-21]), later he becomes one of the few people who are willing to take action on Tom’s behalf, speaking out in his favor at the trial.
Mr. Link Deas rose from the audience and announced: ‘I just want the whole lot of you to know one thing right now. That boy's worked for me eight years an' I ain't had a speck o'trouble outa him. Not a speck."
"Shut your mouth, sir!" Judge Taylor was wide awake and roaring. […] "Link Deas," he yelled, "if you have anything you want to say you can say it under oath and at the proper time, but until then you get out of this room, you hear me? […] I'll be damned if I'll listen to this case again!” (19.89-90)
While on the one hand it’s admirable that Mr. Deas wants to support Tom, in speaking out of turn he risks causing a mistrial, which could put Tom in more danger by drawing out the process even further. But since even with a trial that follows the rules of order, Tom is unjustly convicted, perhaps Mr. Deas has the right idea in breaking the rules to speak on the side of truth.
After Tom is killed, Mr. Deas continues his support of Tom’s family. He creates a job for Helen even though he doesn’t really need her help, as a personal attempt to make up for the injustice of the system. While he doesn’t do much to change the ways in which the system is broken, he does make a significant difference in the life of Helen and her children by protecting her from Ewell.
“As Mr. Link came out of his store he saw Mr. Ewell leaning on the fence. Mr. Ewell said, "Don't you look at me, Link Deas, like I was dirt. I ain't jumped your-"
"First thing you can do, Ewell, is get your stinkin' carcass off my property. You're leanin' on it an' I can't afford fresh paint for it. Second thing you can do is stay away from my cook or I'll have you up for assault-"
"I ain't touched her, Link Deas, and ain't about to go with no nigger!"
"You don't have to touch her, all you have to do is make her afraid, an' if assault ain't enough to keep you locked up awhile, I'll get you in on the Ladies' Law, so get outa my sight! If you don't think I mean it, just bother that girl again!"
Mr. Ewell evidently thought he meant it, for Helen reported no further trouble. (27.8-12)
Ewell tries to hide behind the letter of the law by not staying away from actions that are obviously criminal, but Mr. Deas sees what he’s really trying to do: terrorize Helen in a way that might make her stay home or leave Maycomb altogether. Mr. Deas’s threats raise the question of what would have happened if Helen herself had taken the matter up with the law (though after what happened to her husband, it’s not surprising she doesn’t want to): would she have been able to get effective support without a white man backing her? Like Tom, it seems that for Helen her legal rights are dependent not on what the law says but on the white men who enforce the laws, or fail to do so. While Mr. Deas does act on the side of justice, making Helen’s safety dependent on him raises the question of what would have happened if he hadn’t been willing to take on Ewell.