I personally always thought and was surprised JR did this. Simply because I would have thought he would have rather had Clayton in jail rather than "bed Laurel"
Remembering the things JR said about Clayton, always referring to him as an outsider, saying "if he dies, he dies" in a telephone conversation when Clayton was in the hospital for a heart problem, you'd think so, wouldn't you? You'd think he'd prefer Clayton went to prison.
I think the reason they didn't go in that direction is they always tried to make sure that JR had a certain amount of likability, since the audience liking him, or at least liking certain things about him was one of the major factors that made Dallas such a success. As far as I know, TV shows having a central character like JR - "the cool bad guy" - was something that hadn't been done before at that time. It was a groundbreaking concept that lots of shows took and tried to apply to one or more of the characters in their shows, with varying levels of success but never to the level of success of what Dallas did with JR.
Usually the innovator in some particular style of art or entertainment remains the best. When a rock band with a unique style became tremendously successful, inevitably there would be lots of people who would come along and try to copy them to achieve that level of success. They almost never were able to achieve it though because nobody can do Van Halen better than Van Halen, nobody can do AC/DC better than AC/DC, nobody can do KISS better than KISS, nobody can do The Rolling Stones better than The Rolling Stones because they were the originals. In music, for a copier to do the same thing the original did, but as good or better than they did it is either impossible or damn near impossible. I don't know nearly as much about TV so I can't say for sure, but I'd think the same idea applies, at least to some degree.