The market will always need copywriters, regardless of the strength of the economy. It was much easier to sell a good product with subpar marketing in the past. But globalization has expanded the market and competition driving up the need for good advertising. Consumers can only distinguish between products based on advertising; a company must employ copywriters to send a clear and consistent message to their target audience. Copywriters are even needed when a company loses sales because cutting the advertising budget will result in even weaker sales. If a recession comes along, demand may drop a little for copywriters but it will pick right back up when the economy turns around.
The growing size of the Internet had produced a large market for copywriters as well. With over four billion websites currently on the web, it is very difficult for a company or person to get their website to show up under a search (such as with yahoo.com). A good copywriter is needed to "index" the site in order for it to show up, they do this by appeasing searchers and search bots with good writing. There is a huge market for copywriters to perform Search Engine Copywriting.
Copywriting allows you to work for a company or for yourself. You can find work all around the country and demand will keep pace and grow with the economy. Over 500 jobs are available to copywriters on the site Monster.com, and this is only the tip of the iceberg. There are many other mediums to find copywriting work, but this should help you see the great demand for a copywriter.
This article should help you see that a copywriter will always find work despite the health of the economy. Even if the economy is in a recession, some companies' sales increase and they thus need copywriters. The whole of the market will ensure that a copywriter has plenty of work.