I'd want data. The system I work on does in fact spawn a thread to handle each and every connection and in fact each connection thread spawns numerous child threads to exploit available parallelism within the request. The code is fully blocking and linear and anyone can read it and see what it is doing. The mentioned system is one of the largest public networks services on earth.

I am very skeptical of the idea that you must not handle thousands of connections with a thread per connection. High tens of thousands of threads per core is the minimum level where I would start to worry.