There are respected, successful, talented, effective trainers at nearly every point along the spectrum of “hardness.” (Personally, I think the very best trainers tend to have superb balance of the various principles along the majority of the spectrum, and can shift themselves as the animal and situation demands, but that is a topic for another day.)
Those nearer the “hard” end tend to espouse messages around strong leadership and boundaries, and not letting your animal become pushy, spoiled, wild—they tend to be big on clarity and firm authority.
Those nearer the “soft” end tend to espouse messages around listening to your animal, helping him find calmness and relaxation, making sure his needs are met and he is comfortable, soft, relaxed—they tend to be big on empowering, motivating, encouraging.
In general, I think owners who are near the soft end of the spectrum would improve the most by spending the majority of their time listening to trainers who are nearer to the hard end, and owners near the hard end would improve the most by primarily listening to trainers nearer the soft end. Not that anyone should feel compelled to go “too far” outside what seems ethical and right to them–quite the opposite, it is important to work with trainers whose techniques make sense and feel good and correct to you, but generally listening to trainers a bit in the direction opposite your leaning will maximize growth and learning and help you to become a more balanced trainer with greater breadth and depth.
What is interesting is that the opposite tends to happen—soft owners are drawn to soft trainers whose messages sound and feel familiar and comfortable to them, and so they reinforce or exacerbate their inherent imbalance; and hard owners seek out hard trainers who tend to reinforce or exacerbate their innate proclivities.
This is also true with politics, metaphysics, media, life: it is important to seek out those whose central ethics and ideals overlap with yours, but if you constantly surround yourself only with like-minded experts who affirm and reinforce your inclinations, growth is slower and less certain than if you also seek out, and genuinely consider, those whose views will push you to question your tendencies and consider alternative perspectives.