I'm going to chime in here, but my views are probably very different than those stated above. Haha. I just think it's a good idea to see various viewpoints to try and help you find what you feel most comfortable with. (: Like you said, many have different views on the spiritual world and it's important to keep an open mind regardless.
First of all, I'd like to stress that there really is no true answers to these questions or how spirits are, what they do, etc. We can only speculate and go based off personal experiences or try our best to believe in others'. So while we can answer with our opinions on the matter, we can't give you a 100% factual answer to your questions. I say this because the spiritual realm isn't an exact science, like chemistry. You know? There really are so many different opinions on spirits, what spirits are, where they are, how they communicate, what to do to communicate, etc. We don't have any idea one way or another because we're still exploring into this realm on our own. If we had all the answers, there wouldn't be any spiritual debate on whether they're real or not. ;D
As for my own personal beliefs, I don't believe that communication itself is inherently dangerous nor is it a bad thing necessarily. I agree with Seraphin that you don't want to call upon those that don't want to be disturbed. However, if you simply want to try and communicate there is nothing wrong with that in my opinion. My reasoning for this is that there may be someone who DOES want to speak to you and they may not know how to contact you first. You know? You just need to make sure you go about it in a way that isn't going to bring forth spirits/entities that do not wish to speak with you or anyone. However, like BabyBear said, protection is incredibly important if you plan on doing any kind of communication.
There may also be some spirits that simply just don't want to pass on and enjoy hanging out in this world, and they may just be looking for someone to talk to.
Now, the way you go about doing these things is incredibly important because there ARE bad things out there that CAN do harm to you. It's just a matter of ensuring you do not let those things in and if you do, knowing how to handle it.
I did write a whole thread about this, if you'd like to get some more information. Though, it's focused more on spiritual communication:
Spirit Communication: A How To.
Like it's been stated, doing this in groups is probably your best bet but it's up to you to do this the way you're most comfortable should you ever choose to attempt it. (: I've been working with this for a long time, as I'm sensitive and have spoken with spirits in the past. The good news is that the bad ones are few and far between. I know quite a few people who work within this kind of "field" and they've never encountered anything negative. You just have to make sure you go about things in a way that is safe and protective!
I'm also a paranormal investigator, so I have opinions and views from that side of things too. If you ever need anymore help, don't be afraid to ask or PM me too. I love helping with this kind of thing! Haha. (: