Well, Greg, since you claim to be a bit slow on the uptake-- (though a master of pointless foul language--facts and logic, not so much)--- , your reference should have been "Et tu, Rone?", and since the source of your attempted Latin phrase is painfully obvious, the original meaning is also obvious--and does not fit your context.   It's also not the nominative case. ( I'm putting myself in the second declension). You may want to brush up your Shakespeare, so to speak.

As for everything coming from McPherson, your reading skills need a bit of work. I've cited several other books.

And you also may want to broaden your own reading a bit.

You seem to believe many Northerners saw slavery as an economic threat to their livelihoods.   You have given precisely zero evidence for this.   Whereas it is painfully obvious that most Northern unskilled laborers were just fine with slavery in the South; they did not fear competition from Southern slaves. However, faced with the prospect of large numbers of freed slaves, the Northern laborers did have a deep fear; the prospect that huge numbers of former slaves would come North and take their jobs. This fear was fanned by unscrupulous politicians like Democratic Governor Seymour of New York. Yet again, the perfect illustration of this is the 1863 draft riot.

If you do in fact have evidence for your assertion, I'm sure we'd all like to hear it--with exact quote and exact source.   Not that we don't trust you to give a balanced perspective, of course.

For somebody who supposedly has been in the field for decades, you seem to have a remarkably unnuanced approach, and even an incurious mind. But I'm sure that's just an unfair perception, which you will remedy.