On HN, and such, people call everything a side project due to fear of criticism. If you say "it's a side project", and people criticize it, you can say "it's just a side project".
Statements like "everything is unique" are very obfuscatory. How am I supposed to make any decisions? Yes, certain parameters might be different but a universal truth accounts for this.
Instead of posting platitudes, post a rebuttal. Post a counter-example.
1. The business world is competitive.
2. Some people are working on their ideas full-time.
Then how is it not a huge disadvantage to not be working full-time on your idea? I'm very curious how people who advocate for side projects think about this differently? With ones they hope will become successful businesses at least, other side projects, such as open source projects, make perfect sense.
I also think that this meme is alive because people are working on their startups and are hoping for them to take off. In some sense, they repeat what they hope is true.