[Bubba Ho-Tep]

Of course, while Rawle does recognize the possibility of secession, he's pretty stern in warning against it, on both practical and moral grounds:

Evils more alarming may readily be perceived. The destruction of the common band would be unavoidably attended with more serious consequences than the mere disunion of the parts.

Separation would produce jealousies and discord, which in time would ripen into mutual hostilities, and while our country would be weakened by internal war, foreign enemies would be encouraged to invade with the flattering prospect of subduing in detail, those whom, collectively, they would dread to encounter.

(...)

In every aspect therefore which this great subject presents, we feel the deepest impression of a sacred obligation to preserve the union of our country; we feel our glory, our safety, and our happiness, involved in it; we unite the interests of those who coldly calculate advantages with those who glow with what is little short of filial affection; and we must resist the attempt of its own citizens to destroy it, with the same feelings that we should avert the dagger of the parricide.

[Titus Quinctius Cincinnatus]

Of course, as did most everybody who wrote about the issue, both before and after the ratification of the Constitution. Warning against the dangers of dissolving the union is not the same thing as saying it cannot be done. It's saying that it shouldn't, unless you think you have a jolly good reason to do so. The Founders felt pretty much the same way about the union the Colonies had with Great Britain, which is why the Declaration of Independence contains such a long listing of abuses to the Colonies by GB. The Founders felt that they had to provide, before God and the world, sufficient cause to show that they were legitimately exercising the right to break the political bonds the Colonies had with the home country. As history records, they indeed DID feel they had such cause, and acted accordingly.

The Southern States felt that they, likewise, had sufficient cause. The issues involved - slavery, tarriffs vs. free trade, sectional antagonisms, interference in internal State affairs - had been going on for decades. The Southern States didn't make their decisions on the spur of the moment, they were responding to decades of feelings (right or wrong) that they were getting the shaft from the other sections of the country. Some of it was the issue of the extension of slavery - though even then, slavery itself was not so much the issue as was the balance of political power at the federal level through the addition of new States carved our of slave and free territories. Some of it was tariffs vs. free trade. The North wanted tariffs to protect its manufactures, and the South wanted free trade so as to sell its agricultural products to Britain and France. The North wanted tariffs for two reasons - to make money off of abundant Southern exports through federal taxation, and to "encourage" the redirection of Southern cotton away from industry in Europe and towards the Northern States. And, people being people, a lot of it was just hurt pride, on both sides. The North and South were involved in a giant urination match with each other for decades, and the South felt that the balance of power was going against them, and that nothing they said or did would ameliorate the situation, which they thought was going to go increasingly against them and overwhelm then with "Yankee interference". In short, the South DID feel they had legitimate cause, a long train of offences (real or imagined), to justify dissolving their bonds to the union.