They gathered a bunch of data and had a meeting in Asilomar (a pretty conference center in the middle of nowhere on the CA coast). In addition to the scientists who actually had the technical ability to splice genes (~100 humans at that point had the requisite skills), some lawyers and philosophers also attended. They argued a bunch. And at the end of the day, they agreed on a voltunary moratorium on splicing, even though the argument for immediately, direct harm had not yet been made (precautionary principle).
Very reasonable predictions were made. Some of the more irresponsible claims were tamped down as being overly irrational. Some basic rules were applied on how to minimize collateral damage. Some strong rules were applied on disease-causing experiments.
It seems, looking back with the luxury of historical distance, that they chose wisely. It was probably because the level-headed people who focused on clear and present dangers, not absurd hypotheticals, managed to win the day.
Today, the logical conclusion of those decisions are just starting to be felt; we now have technology that permits us to make germ-line modifications (those are permanent, inherited changes), and we're starting to do actual trials with newly born children (this is, IMO, one of the most extraordinary moral and philosophical developments of my lifetime).
It's unclear to me whether CS has the same level-headed maturity that lead to this. Nor do I think people in CS can really predict the indirect outcomes of their technology. Instead, I think CS people have an obligation to push the technology as far as it can go within a community-determined set of boundaries, and report the direct implications thereof to the general public, who will then (indirectly through democratic mechanisms) create laws that restrict certain applications.