There were plenty of Catholic bigots in the South as well. Masons don’t hold exclusive territory over that term. Rather since Masonry was an organization made up of “leading men” of many communities, it was only logical that the prevailing segregationalist view would be echoed by lodge members.
That being said, the Catholic Church has REAL reasons to condemn Freemasonry. It is essentially a heresy and to take the oaths that Masonry requires you to take, you are basically disregarding Catholic teaching. Freemasonry does not, to my knowledge currently exclude Catholics. On the contrary, we’ve had plenty of misguided Catholics on here post about how they are Masonic lodge members and don’t understand the Church’s prohabition. However, depending on time and place, there have been varying degrees of anti-Catholic setiment in the organization.
You might look into the P2 conspiracy to see how even in modern times, certain Masons have used (or misused) the organization for less than honorable means.
KofC, on the other hand, requires you to be a practicing Catholic. It is a men’s organization that encourages faithfulness to Church teaching, and places a strong emphasis on charitable works. There is nothing in its teachings or ceremonies that conflicts with Catholic teaching.
Perhaps you should search for past threads on freemasonry and knights of Columbus here. There are many!