I have to agree with you both, excellent topic Paula and right on Maresa, It's the personalities and attitudes of the sensei and students that create the environment we train in. If they have bad personalities then that creates a bad environment, if the sensei is excessively brutal then many of his students will also be and then you have a fearful environment.
When I first visited my dojo I was amazed by the comaradery and friendship between the students and sensei. Hearing the sensei use a joke to illustrate a point on self defense and then hearing laughter on the mat also seemed a far cry from my memories of karate as a child. Because of this and of course the fascinating things they were doing, I knew then that I wanted to train with these people and Im so glad that I did and still do, I love my dojo and my dojo-mates, they are my second home and family.
I suppose a lot of factors could extinguish the spirit of a dojo, perhaps losing a sensei or a sempai, or if a prominent member of the dojo is going through some personal troubles. Perhaps if some students attitudes change and challenge the status Quo. Sometimes it would be up to the sensei to rekindle it/fix the situation, sometimes not? I would suppose it's up to everyone who cares about the dojo, I know if anything happened to extinguish the spirit of our dojo, that we would do everything in our power to rekindle it. We've come through some rough times recently, but we are stronger than ever