Why do some testers feel that they do not have to follow the test script blindly and they know better than that? Is asking them to stick to the test script, insulting to their intelligence? I am not too sure about the answers as it has many psychological and social layers.
I think there is a need to identify the inherent nature of any individual tester, if some feel that they would do better doing exploratory testing then we need to respect that. At the same time, effort must be made to validate their claim to assess their aptitude. Those testers who wish to be 'free-birds' should be not be forced to stick to pre-decided test script, it will certainly suppress their creativity. While we go about doing this, we got to ensure that we are not producing 'rogue-testers' (apologies if anyone is offended by this term). As saying goes from Spider-man movie, 'With great power comes great responsibility', so we need to be careful that we are not giving power into reckless hands. I would not like to use the term 'adhoc testing' as synonymous to Exploratory Testing, 'adhoc' for me signifies careless, sloppy and chaotic, things we do not relate to testing.
Now who would be ideal candidate for exploratory testing: someone who is well-verse with the application functionality and design, someone who has strong intuition, someone with strong analytical skills, someone who can design and modify the test design on the fly.
Exploratory Testing need not be against the ides of test scripting, rather it should be used in combination with test script based testing. And each of these teams would require testers with specific temperament and ability for successful execution.