It has never been "unacceptable" as long as you have the means of buying them. Empress Josephine was said to have owned 521 pairs of shoes. Other upper-class women will likely own many pairs of shoes for different occasions since wearing the right attire from head to toe was much more important back then. Most people did not have many shoes simply because they could not afford multiple pairs of shoes. According to Linda O'Keefe's Shoes, various inventions during the Industrial Revolution that aided the mass production of shoes, including sewing machine, large scale loom, roller fabric printer, etc has made shoes cheaper and more accessible to everyone.

Shoes haven't really been expensive, thankfully. In the late 18th century they cost around 5-8 shillings for a ladies pair. That's about a days wages for a journeyman shoemaker, and they would make a comfortable living. They're also already being mass produced by that point by Lynn, Hose, Didsbury, Gresham, and more. Mind you, these are very fashionable shoes. "Common" shoes of lower quality could be purchased for less, and in some more rural areas of England and Europe wooden soled shoes were still common as well. Prior to this time remember that leather is cheap, not a luxury like today.

In the second half of the 19th century, heels come back into fashion. This goes hand-in-hand with the use of machinery to produce them. It also doesn't take long for the assembly to be mostly done with gluing the layers together rather than stitching. The quality of leather also begins to drop steadily. Even though shoes are cheaper in price, they're also cheaper in quality. You may be able to buy five pairs a year instead of three, but those will likely wear out by the time you get a new pair and are less easily repaired than stitched soles.

The next big change is the use of a rubber sole. Men's shoes begin testing this out at the beginning of the 20th century, but women's shoes take a little longer before they adapt it. Today we don't have nearly the problem of wearing through our soles that previous wearers did with leather. Our leather soled shoes are also hardened and stiffened so that they no longer flex with the foot. We've made up for poor quality supplies and construction by changing the structure and goods used.