Kernel maintainers are volunteering their time and effort to make Linux better, not to be entertaining test subjects for the researchers.
Even if there is no ethical violation, they are justified to be annoyed at having their time wasted, and taking measures to discourage and prevent such malicious behaviour in the future.
Given the importance of the Linux kernel, there has to be a way to make contributions safer. Some people even compare it to the "water supply" and others bring in "national security".
> they are justified to be annoyed at having their time wasted, and taking measures to discourage and prevent such malicious behaviour in the future.
"Oh no, think of the effort we have to spend at defending a critical piece of software!"