Why checkbox couldn't be checked by javascript instead of the user?

Few questions:

Why checkbox couldn’t be checked by javascript instead of the user?
Why after checking checkbox just simply not hide it from user?
Why the problem of spam should be solved by users?
Why user should prove that he is not spammer?
Maybe it would be better for spammers to prove that he is real user?

Having javascript on the client is already a proof that user is not spammer.
Spam bots haven’t javascript because it is not browsers.

http://wordpress.org/extend/plugins/growmap-anti-spambot-plugin/