I get where they're coming from, there are some trails here that have existed longer than the cookie cutter neighborhoods that were built around them (I'm 40 and started riding those trails when I was like 12) and they advertise the "walking trails" nearby. Not so bad when the walkers are on the clearly marked walking trail part, but when they wander onto the mountainbike trail part and then act shocked and angry that there are bikers moving fast on the clearly-not-for-walking trail it can be annoying. Also the walkers who have their off-leash dogs with them who get mad at me because their off-leash dogs chase me.
One thing both walkers and bikers can agree on though is that the horse riders who keep poaching the bike and walking trails are the fucking worst. They tear up the trails and often scoldingly tell the people who are using the trail properly that they need to make distance for them because their horse isn't "good" around people.