I don't see any reason for private companies to venture into space. Experiments? Pay NASA to do them. I can't see space tourism taking off, seriously. I mean, I'd rather pay a hundred thousand to Antartica and see penguins than to pay a few millions to go to Mars and see Martians. Same goes for looking for resources. There just aren't that many modern resources that aren't cheaper to get on earth. Oil would be cheaper to find in Africa in the next century than finding them on Mars. And even then, transportation price would be ridiculous.. and massive oil space tankers would be rather nasty.
So, I'd kinda tick out private corporations. But if some technological breakthrough manages to make space travel cheap, then it'd be a whole different situation. Space elevator isn't all too unlikely. My vote's on there being space navies. Simply because countries want to colonize space. Being the politician who got USA to claim half of Mars and Phobos goes nice on your resume and history books. Space navies are going to be extremely expensive, but if you find some useful resources out in space, it's not impossible.
You could look to history as a guide, but there's some differences. For one thing, you can't live indefinitely in some foreign planet on coconuts, and there's nobody from space bringing you valuable resources. It's going to be very difficult to find a foreign planet even worth colonizing... that's probably why we're sending so many robots to collect frigging rocks.
I wouldn't brush away space pirates if the thing takes off, though. It's certainly not as easy as in sci-fi stuff, but possible. Piracy, like any other theft, works when it's possible and lucrative. If you have a space vessel with lots of powerful weapons against a civilian vessel with no defenses, it could well happen. You don't even have to board the ship.. anyone would be terrified of being shot out in space and away from repairs.
Air piracy is just not easy. Plane cargo is very poor, compared to the millions you can get from hijacking a ship. Airplanes are also very fast with very short trips, and are always in safe territory. It's just not feasible to chase most planes, and the fuel costs more than anything you could steal. Space freighters would probably have a lot more bounty and much more time between departure and arrival. They'd still move at near light velocities, so it's going to be difficult to follow one, much less capture them.
but more importantly because communication is such that you'd be instantly identified and responded to
This alone could be a huge contributor to space piracy. Communication is going to be absurdly difficult in space. Doppler effect makes communication while travelling tough. You'll be light-hours to light-months away from other people, reception will be extremely poor. Worst of all, it's going to be tough for pirates to latch on to freighters, but even tougher for enforcement ships to latch on to pirates.