And of course they mentioned reasons other than slavery, like Constitutional rights and state's rights. The problem is, they saw owning slaves as among those rights.
You expected them NOT to note that it was the other side which violated the constitution? What they really hated was actually constitutional....namely the way they were economically exploited in favor of Northern business interests. The North offered slavery forever but did not offer to stop screwing them over economically. They turned down the offer. That tells you all you need to know about the real motivations of both sides.