Yes, no, maybe so.
There are a couple major things in play here.
"Too dangerous" is very subjective of a term. It really depends on what the JS is being used for. JS is merely a tool.
The most common (and perhaps most damaging) is called a cross site scripting attack where malicious JS redirects traffic. This traffic can be spoofed and therefore appear as trusted/secure but it really isnt. Thus, I say this attack is 'dangerous' because otherwise secure and meaningful communications (passwords/logins/etc) can be intercepted.
Additionally, JS could initiate many other kinds of targeted malware but that 'danger level' is determined by the actual malware.
Once again, you question is broad and subjective...
btw, if you are really concerned consider using something like NoScript to selectively allow JS.