Good point, and we can see this pendulum swing during the Dallas run.

We forget now, but the original miniseries was decidedly darker. It has a Shakespearean tragedy to it. The original Jock was hinted to have built his empire by bankrupting his competition through dirty deeds.
J.R. was a ruthless businessman by necessity. He had to live up to Jock's expectations (and never quite could). You actually felt sorry for J.R. in the early episodes, "Well, Daddy. I just thought one time you would have been proud of me."

Then, as our national mood lifted from the morass of the 70's, the tone of the show lifted as well.
J.R. became the villain that we often rooted for. Or at least tuned in to watch.
Ray became a Ewing, and a millionaire. Donna bought an oil field and named it Krebbs One. Bobby showed he could run Ewing Oil. There was even humorous patter between sworn enemies:

Cliff: Well, J.R. I've got great news for you.
J.R.: Oh, you've been diagnosed with a fatal disease?

HA! That magnificent bastard.

And there were storylines that were a little outlandish. And we had fun with them. And we all spent one memorable summer wondering, "Who shot J.R.?"

It was fun, and light hearted. The series mirrored that time in world events.

Then, as the end of the series approached, things moved darker once more, reflecting the dimming view toward large companies. The Exxon Valdez was traveling in the most pristine, deep blue water you can imagine inside of Prince William Sound. The oil tanker struck a reef spilling ten million gallons of oil. (37,000 metric tonnes for our European members here). People who fished all their lives, who never dealt with Exxon, had their livelihoods ruined.

Big corporations were expanding, and putting mom and pop shops out of business. Executives were laying off workers at the same time they were handing each other huge bonuses.

We stopped rooting for the magnificent bastards who walked all over people.

And the end of the series reflected this. The Shakespearean tragedy came full circle, with J.R. ending the series all alone, with a bottle of bourbon in one hand and a gun in the other.

 

It's fascinating how @Lastkidpicked and @Kenny Coyote drew parallels between the tone of "Dallas" and what was happening in America at the time. Very clever observations!
I read an article by Stephen King on his opinion on why certain things in popular culture catch the public's interest. According to him, evil or scary children, especially girls(The Exorcist, Carrie, The Omen, etc) were popular in the U.S. during the late 60's and the 70's because they reflected an unconcious fear or unease with the youth and feminist movements. In Germany, he believed zombie movies were more popular at the same time because they reflected a subconscious fear of being haunted by the past.
The accuracy of Mr. King's theory is, of course, open to debate. However, the subject of art reflecting life, life reflecting art, or various degrees of both, is intriguing.

 

Makes one wonder how many of us could do it, just as the battle for Ewing Oil makes one wonder if we ourselves would
have behaved differently from Bobby. I believe you brought up that very interesting point.