It's not that there's anything "wrong" with them, it's more that as an introduction to a topic they leave something to be desired. I often find that for this type of a paper opening with a question is very effective. It gets the reader thinking about your topic and almost immediately engaged. Instead of telling the reader that the 50's were considered the golden age of marriage, show them.

Something like "When you think of an ideal marriage, what is it that comes to mind?" (You may want to replace the you depending on what level you're writing for and your teacher's preferences. I find that some teachers will really look down upon you if you address your reader directly in a paper, while others may encourage this type of writing.)

You can take something along those lines and work the rest of your ideas into it.

Also I'd elaborate on the unhappiness. Don't make the paragraph your essay, but make it a best of what's to come. Introduce your essay and introduce what you're going to be talking about. If they were unhappy because of rampant alcoholism, spousal abuse, and borderline slavery, then say so...this is where you say that, later on you can elaborate on each point and explain why you're right. Don't be afraid of a long introductory paragraph...in some of my longer papers I've had first paragraphs that were over a page long...if you need the length, take it. You're going to be punished harder for having too short a paper than you ever will be for having too long a paper (unless you're in a technical writing class where brevity is king).