I personally feel that a therapist who is always accepting and positive in their interactions with me is not encouraging progress much more than I can do alone. I think it also depends what sort of treatment and attitude someone has found helpful and inspiring historically... I have a history of being surrounded by smart, kind, independent and outspoken significant people who like to say what they think. When I say "challenging", it indeed means honest feedback and providing an opinion (even if it's not very accurate), not so much claiming that what I do is wrong and I should not be doing it. But also, when I engage in self-destructive behaviors that defeat my goals and only cause problems, I do appreciate pointing it out, especially if I am in denial. I like when someone engages with me dissecting what my thoughts, feelings and actions mean and provides perspectives that make me think more deeply and in a fresh way. Perhaps we often associate challenge with aggression, but to me, it's more about confidence and constructive criticism, which is a big difference. Of course telling people what's wrong with them and what they should do is hardly very effective except when it's an emergency with someone who presents danger to themselves and others, which require direct interference or when someone is seriously lost and lacks confidence severely. What I really like is when someone uses reasoning to probe into my thought processes and reactions and makes me revise them.

I watched the video Ididitmyway linked and other Gloria videos (with different therapists) before and thought she was perhaps not the best representation of many clients in therapy as she seems to have quite a strong sense of self and confidence.

I like this, too:
I think there is a big difference between criticizing someone's behavior and their self worth or identity. My first therapist used a similar concept when discriminating between "ego-oriented" vs "object-oriented" questions and comments, the latter approach being more protective of the person's self and the first often being shaming.

My second T had an approach to constructive criticism that I liked very much and found very familiar and effective. He is very interactive in sessions and would often share things from his own life that related to my experiences and way of thinking, pointing out both positive and limitations in these rather than in my way of dealing with stuff alone and separately. There was nothing authoritarian in it. It was very effective for me in creating respect and seeing his comments as valuable. I think I found it effective because it's also how I like to relate to others and help, with my students and supervisees, for example... But it does not work with everyone and some people do want/need a more authoritarian approach.