A few years ago, I said: "If your are looking for trouble, put a disc brake on your bike!" But the development continued. I can accept a better braking performance in wet conditions and no more black rim abrasion as arguments in favour of the discs.
But especially trekking riders still have more disadvantages than advantages.
It starts with the brake force: Until disc brakes work convincingly, they need to be run in for quite a while. Those, who never have to brake long downhill roads or under heavy loads, will probably never reach this point. And if they fully brake, the problems start with other components. Suspension forks for trekking bikes are usually much less stiff than high-quality mountain bike forks. The brake force is brought into the fork onsidedly and twists weak forks so much that you have to steer in the opposite direction. In addition, cheap trekking bike forks are not manufactured accurately. Everything vibrates and flaps as soon the brake bites. Speaking of vibration: I do not know one single disc brake which is immune to squealing in wet conditions. This happens time and again and is very difficult to stop. The maintenance of a disc brake asks too much of laymen anyway. Only yesterday, I witnessed further proof of how unsuitable a disc brake is for everyday use: Because of its disc brake, a test bike did not fit into the bicycle stand.