Negativity

Yesterday, my class had to choose a topic for our last research project. We decided, after about an hour (!), to investigate the idea of "Space on Earth". My group, Danielle, Jessica, and I came up with the original idea. We envisioned our planet without an atmosphere. The ozone layer was gone. If that were to happen, what changes would have to be made for humans to survive? What would happen to our water supply, oxygen supply, plant life, and animal life? What about problems caused by ultraviolet rays like skin cancer? The class overlooked our idea for the first part of the discussion which frustrated me since I thought the Space on Earth concept was a great idea. We could even tie the rising issue of global warming into our inquiries. I felt like the idea offered something for everyone.
It seems that there is always that one person in every class that feels the need to find the negatives in every situation. I've been trying to decide how to manage someone like that in my own future classrooms. I think Carl did a good job in providing a list of possible topics for this person to show that the Space On Earth idea was a plausible one. After yesterday, I almost wish that we, as a class, had no say in our research topic. We could have avoided an hour long discussion/argument about what we'd be looking into.
I don't have much patience and so yesterday's class period was challenging for me. I remained quiet for a good part of the discussion process. I tend to be pretty persuasive in my arguments and didn't want to influence the class too early. However, when each topic we visited was getting picked apart, I had to step in. At that point, I didn't even care which topic we decided on, merely that we decide on one at all!! I can actually feel myself getting frustrated all over again just by reliving yesterday's class period.
The big issue that was raised for me yesterday was dealing with negativity in the classroom. This particular individual has been negative in other classes as well and it always bothers me. I can't understand why people cannot just look at the brighter side of life and move on! I've been wanting to say something to this individual since the beginning of the semester, but I don't know how to approach it and I'm not sure if it would be appropriate. Furthermore, how could I handle that problem in my own classroom. People are entitled to their opinions - I do not have a problem with that. I just get tired of having to prolong class discussions because the same person doesn't like EVERY aspect of an idea EVERY time we discuss something.