This has been challenged before, except in the 70’s with the popularity of CB Radios. People would announce where the cops are on high ways. The app is doing the same thing, its freedom of speech like you said.
I look at it as a safety issue. People who are so inclined are going to speed. I generally don't. I might coast along within a few mph of the speed limit on most streets just because I'm not obsessive about maintaining exactly the speed limit. For example, I'll let it roll a few mph over down a hill, and coast back down to the speed limit on the next uphill. On the highway, I'm generally not the fastest or the slowest - I run with what most of the traffic is doing. There are always a few people on either end of the bell curve - blazing along well over the speed limit or wandering along 5 or even 10 under.
But there are those people that do speed significantly, or who feel guilty at even 5 or 10 over on the highway. When they suddenly see a speed trap, they slam on their brakes. I've seen it first hand many, many times (I'm approaching a million miles on the road in various cars, trucks, and motorcycles). That's not safe for anyone following. That's the main reason I warn other drivers. Not to thwart LE, not to save speeders money or points. To help prevent sudden unexpected actions. Best rule of thumb for any relatively new drivers out there: remember the 3 S's. Don't do anything sudden, surprising, or stupid. I've only ever had one accident, and yes *I* violated the "don't do nuthin' stupid" rule.
Waze is only as good as the “Wazer’s” reporting ahead of you.
Drive across OH on State Rte 35 from WV. No traffic, and the State Cop that always sits in the median between Southside and Henderson will surely getcha if your +70.