No, it isn't wrong to use other's ideas. However, to use those thoughts or ideas without those people's knowledge could be considered morally wrong. With some members even saying it might affect the way they interacted with someone. Do you not see any dishonesty in the discibed scenario?
It depends on the circumstances. For instance if you gave me information and I told you I wouldn't share it with anyone, but I did, I would be committing fraud.
If information is "out in the wild" and I use it but made no commitment to you, I haven't breached any agreement.
I view so called "intellectual property" as different from physical property, due to the nature of one being tangible, while the other isn't. I have no right to use your tangible property unless you allow me to etc.
Physical property is unique and can't exist in two places at once, for me to take your property I've potentially deprived you of the use of it.
"Intellectual property" / ideas can exist in more than once place at a time though, so they are not unique in terms of how many people can use them etc.