It is possible that NoScript means allowing JavaScript to run unrestricted in general, not just in the Tor browser but also all browsers, can be very dangerous since after all, it can lead to tracking, XSS, Cross-Site Request Forgery after all. However, if NoScript specifically means allowing JavaScript in Tor browser is dangerous, it could be due to the potential for malicious scripts. Scripts that could accidentally make you install extensions/plugins and compromise your security, scripts that could allow for Self-XSS, or uneccesary scripts that could greatly slow Tor browser down, etc. If the user doesn't have the best security mode enabled, NoScript acts as a second layer of defense for the user's privacy which could be compromised through JavaScript.
TL;DR: NoScript considers using JavaScript unrestricted since it could hurt the user's experience by compromising their privacy through the methods mentioned above. It's not as though it would immediately make you identifiable, but it could increase the chance of hurting your privacy/anonymity. That's why Tor browser has a setting to make the privacy mode "safest" which disables JavaScript, since it can hurt your anonymity/privacy.