"I'm surprised home many technically knowledgeable people on Internet forums still think IPv6 is some niche, unreliable thing."

Where can we read some examples of this

I've read commentary about pros and cons of IPv6 over the years but never anything that suggested IPv6 was "niche" or "unreliable"

NB. The requests is for examples that inspired the quoted statement

In order to have inspired the quoted statement these examples would have to be found in forum comments published before the quoted statement was made

Comments made in response to, i.e., after, the quoted statement would not qualify

The comment from phil21 directly above yours calls IPv6 unreliable.