In his book Clean Code, Uncle Bob quotes Kent Beck about how fragile a premise it is that good code at all matters. Both authors write their respective books on the faith that it is although I suspect it is perhaps more accurate to call it conviction than faith.
It is not uncommon to come across code bases that are undoubtably dirty, messy, or unclean. It is also not entirely uncommon to come across successful projects with a terribly unclean code base. You can’t help but think whether clean code is plain vanity after all.
However, I think clean code ultimately matters because messy code is hard to read and hard to change. When necessary care is not taken writing code, you get messy code and mess tends to multiply and escalate. Messiness can initially be cosmetic but over time (and not a long time is required at all) more material aspects become messy including design and architecture. Small messes don’t stay small for long.
I think an excellent analogy is the Broken Window Theory. The idea is that visible signs of disorder encourages more of it. One story talks about a building which was well maintained for many years. It never got intruded or vandalized. Then one day, an accident happened and one window was broken. The rest of the building was still pristine but, for some reason, the broken window was not immediately repaired. In the following weeks, the building, that for years never got intruded or vandalized, got intruded and vandalized resulting in more broken windows.
Code that looks neglected tends to encourage neglect. Messy code tends to become the foundation for even more messy code. The mess bleeds into design and even escalates into architecture. The mess snowballs.
Between clean code and messy code, we know clean code is better. Yet, we also know projects succeed despite having messy code. Perhaps projects even initially succeed precisely because of quick messy coding. Clean code is practiced on the conviction that it is the right way to succeed. While it may ruffle some feathers, clean code reflects our professionalism and a low barrier to entry is not an excuse for low professional standards.