No - as long identified bugs are critical for the business.
"One can predict the ways in which a software should work but cannot predict the ways in which it will not work."
Testing is inherently an exploratory activity.
If we deprive or even blame an activity for its core characteristic then basically we are turning it into an empty ritual.
Software testing itself essentially is exploratory testing as has been called as in the above link by great testing pioneers in our field .
Any QA should NOT be blamed for finding additional "unplanned" bugs through exploratory testing as long it makes sense for the business. A tester cannot know in advance in which ways bugs will be manifested in the Behavior of an application although positive or as sometimes called "Happy Path" scenarios can and should be identified in the initial planning meeting.
So in a nutshell, positive scenarios can be identified in the initial planning meeting whereas negative scenarios cannot and need to be identified later during actual testing sessions using exploratory approach.
However the extent and duration to which exploratory testing will be used will differ on the nature and business context of the given application as an gaming application might be tested differently significantly rather than a application supporting medical treatment.