"here's a knife. don't hurt others with it."
what's morally objectionable about this?
to me it's morally sensible.

your wish for "without restrictions" is what doesn't make moral sense to me. anything carries restrictions we're normally subject to, from law, from social norms and expectations, from our own consciences.

but some people weirdly think they should not only be entitled to deprive others of freedom, but to use the fruit of our labor to that end. why should it be morally objectionable to tell them that it's not their freedom to do so, and thus refrain from granting them this power over others?

conversely, if they believe it's acceptable to deprive others of something as essential as freedom, how could they object with a straight face to being deprived of freedom?
except that what copyleft does is not to deprive them of freedom (control over one's own life), it refrains from granting them power (control over others' lives), which is not even their freedom to begin with.