The content of Sen. Benton's work is not at issue. It was an example used to refute the notion that no one cared about the Dred Scott decision for a year after it was released.
"Again, the Congress had the power to impeach any of the justices, yet none were impeached."
I like the form of your argument here. Congress, too, had the power to impeach Lincoln for alleged "violations of the Constitution," yet they didn't even think about it. It seems, then, your conclusion must necessarily follow that Lincoln did nothing wrong.
"Millions of yankees did not secede, nor threaten secession because of the [Dred Scott] decision."
Now you're catching on. Millions of 1850's/60's Yankees (or as I like to call them ... Americans) didn't pout or feel their honor was impugned every time the issue of slavery was discussed.
Apples and oranges. Neither President Buchanan nor the federal Congress arrested dissidents. Lincoln had a habit of arresting/interfering with justices of the US Supreme and Circuit courts, state legislators, editors and newspapermen, preachers that refused to pray for him, and anyone else he desired to imprision.