I have played with a ouija board several times and have not had anything bad ever happen to me or the people I was with. I think it can be a lot of fun if it's not taken too seriously. Very often it attracts joker spirits who are there just to play with your mind. Nevertheless some good information can come out of it, to be sure.
As for demons, I am of the opinion that demons and negativity exist side by side with us. Negativity can enter your life only if you let it. If you ask it in, that'll do it. If you fear it, that's another way of giving it power over you. I beliee that if you surround the demon with love, it will greatly weaken its power. After all, it comes from god and will someday return to god.
I completely agree with your statement that if your intentions are positive then energy can not impact you through a Ouija board. Unfortunately, I have had several clients over the years that have opened "portals" using Ouija boards. While they were asking for a relative etc. to appear they got more then they bargained for. At one place they had so much activity after they "played" with a Ouija that it became quite frightening. By the time my group was called out the activity was very negative and intrusive. We referred these clients to several people to cleanse, smudge and bless the place--it took a awhile and the clients were scared.
My objection to Ouija boards is people "play" with them not understanding that they should know what they are doing. I discourage people from using them.