By default, ser2net uses the tcp accepter. This means that your input will be echo’d back to your terminal. For most use cases, that sucks. Modify it to the telnet accepter, and the issue is gone. For example, use:
connection: &con0096
accepter: telnet,0.0.0.0,2000
enable: on
options:
banner: *banner
kickolduser: true
telnet-brk-on-sync: true
connector: serialdev,
/dev/ttyUSB0,
9600n81,local