One of the governments primary jobs is protecting you from aggressors. You may not agree with the method a government uses but that doesn't change it's job description. So when they come for the terrorist they are pursuing a legitimate governmental role.
When they come for the whistleblower and illegal alien it becomes debatable whether they are pursuing a legitimate governmental role. It's very definitely an apples to oranges comparison there.
The problem, and what bandushrew is saying, is that purposes can be flexible. Once a system or method is legitimised, legalised or even routinely used it can be repurposed for other means. That's the true message of the OP's post - the "coming for" is the method in this case, while the people listed are the individual purposes.
When they come for the whistleblower and illegal alien it becomes debatable whether they are pursuing a legitimate governmental role. It's very definitely an apples to oranges comparison there.