Because the denialists attack the value of climate science, so "non-denialists" are frustrated by their criticisms?
The charge of 'denialist' has the potential to raise the temperature of any discussion of climate change by a few degrees. It is usually invoked by those who are frustrated either with criticisms of the trustworthiness of climate science or else with obfuscation about the desirability of taking action on climate change. It is also a claim that often triggers equally vehement claims of climate change 'alarmism', the result being a collapse of discussion into the simplistic binary trope of good versus evil.
(not a teacher)
Your assessment is correct.