Copyleft licenses are not “restrictive”
One may observe an axis, or a “spectrum”, along which free and open source software licenses can be organized, where one end is “permissive” and the other end is “copyleft”. It is important to acknowledge, however, that though copyleft can be found at the opposite end of an axis with respect to permissive, it is not synonymous with the linguistic antonym of permissive – that is, copyleft licenses are not “restrictive” by comparison with permissive licenses.
Aside: Free software is not synonymous with copyleft and open source is not synonymous with permissive, though this is a common misconception. Permissive licenses are generally free software and copyleft licenses are generally open source; the distinction between permissive and copyleft is orthogonal to the distinction between free software and open source.