SWTOR PVP is not that great, in fact it's just a little worse than WoW's, in my opinion. So it's no privlege to do more than 3 Warzones.
That being said, a free player trying out the game, you know, a potential customer, won't be so keen to give you their money if all they can do is get a small sample of PVP (during wich he can get totally owned by organised and better geared teams).
All I'm saying is let people join PVP, reduce their rewards, let them gain marks 3 times a week or something like that. Just don't shut the door in ther face like this. As I said, your PVP isn't that great, it's not the strong point of this game, so I don't see why this restriction was imposed.
What I get from this is I want to play more for free so why don't you let me. If PVP is not that great to you then what does it matter if you get to play more or not?