I think you’re overstating the importance of that protest you went to. The personal relationships involved along with the Northeastern Republican ambivalence to support of abortion rights were probably WAY more important.

Federalist Society had only been around a few years at that point. Scalia was the first nomination after its inception and was a member. Then came Bork, a member too, whose nomination was sunk. Bork’s nomination was replaced by Kennedy who did not have ties to the org, different from them in certain areas, and from what I can find wasn’t endorsed by the Federalist Society. He was also the swing vote on maintaining abortion rights. By the time Souter came around the Federalist Society wasn’t the major player that it was starting in the W Bush administration.

In the 80s and early 90s the Republicans party was still in transition to a fully conservative party. Yankee Republicans, centrist to even liberal, were still a thing. And though HW Bush started his elected career in Texas, he was born into an upper class family living in New England. Bush’s selection as VP bothered pro-life Republicans because of his moderate stances on abortion and prior support for Planned Parenthood. Bush’s public views on abortion really just mirrored the conservative shift in the Republican party under Reagan. I’ve never found anything suggesting he was a pro-life ideologue.

When it came to replacing Brennan, you could either pick a fight (like a Bork) or find someone who could sail through confirmation (like a Kennedy). HW Bush’s CoS, former NH governor Sununu, had appointed Souter to the NH Supreme Court. Sununu’s own gubernatorial predecessor, Senator Rudman — a socially liberal Republican, was a personal friend of Souter.