Silence is the worst kind of feedback
This post about dealing with negative feedback is spot-on:
Silence is the worst. Negative feedback is just part of the process. You’ll need thick skin (every startup founder needs thick skin and a healthy dose of delusion). Try your best to avoid the crazy up and down roller coaster that comes with good and bad feedback. Focus on learning. Focus on extracting the value from feedback, and moving forward.
It's important to respond to your colleagues, even if you think someone else will. Silence is the worst kind of feedback.
If you don't like what someone's doing, tell them. Nobody learns if nothing is being communicated.