Intellectual property laws protect most functional and non-functional designs traditionally produced by men, such as mechanical inventions and scripts for plays. But, intellectually property laws do not protect most functional and non-functional designs for matters that were traditionally produced by women in the home, such as recipes and fashion designs.
Economics has gotten ahead of tradition. Recipes and fashion designs are now big business. And, while recipes can be protected as trade secrets that competitors must at least reverse engineer. A fashion design, almost by definition, is disclosed in every article clothing produced in that design.
As a result, while unauthorized knockoffs of greatly admired designs governed by patent and copyright laws are mostly economic only when the designs enter the public domain, knockoffs are common in the food service industry and are even more dominant in the area of fashion where they are a major economic force.
Certainly, the lack of intellectual property protections for fashion have an impact on the way that the industry is structured. Certainly, top fashion designers make less money per design as a result. Certainly, this makes the skill involved in being able to rapidly replicate someone else's design more valuable.
But, a lack of intellectual property protection almost certainly makes far more designs available to far more people at an affordable price.
It is also not at all obvious that the total amount spent on clothing is materially different as a result of a lack of intellectual property protection. Indeed, one economic hypothesis with wide currency among fashion industry economists is that the lack of intellectual property protection increases total spending on fashion. This is because these economists think that a lack of intellectual property protection causes fashions trends to shift more frequently than they would otherwise, and because clothing is often replaced not because it isn't functional any more, but because it is no longer fashionable.
And, while the amount of money that a fashion designer makes per design is surely less without strong intellectual property protections, the high fashion turnover rate and high demand for people who can copy original fashion designs, may mean that the number of designs per fashion designer may be greater, that the number of fashion designers employed by the industry may be greater, and that fashion design may be less prone to the "winner takes all" tendencies that pervade most aspects of our economy.
The bottom line is that while intellectual property laws have significant economic effects, that a lot of those effects have to do with the distribution of income within the industry and how the industry is organized, rather than being an existential problem for an industry.
We know from history that the same is true in the arts. The music industry including music composition, for example, managed to flourish long before music copyright protections became available in the 20th century. Shakespeare and the Greek playwrights managed to make comfortable livings for themselves in the absence of intellectual property protections.
Technology has changed the equation by making it much cheaper to make large numbers of high quality copies of a design at a low price. But, let's not kid ourselves. For example, before people were pirating novels, there were still institutions like libraries which allowed hundreds of people to enjoy a book for the price of a single printed copy, profoundly suppressing demand, and the publishing industry survived anywhere despite the loss of revenues.
The question of whether intellectual properties laws help or hurt the economy in particular contexts remains an open question. But, it is empirically well established that an economy can function quite well without them.