Firstly, although Romeo and Juliet are the protagonists of the play that doesn't mean they do not share in some of the blame. Their courtship was very brief, the play spans less than a week, so it could be argued that they rushed into their marriage without properly planning anything or taking the time to think of the consequences. It doesn't appear they had any plans beyond their wedding night yet they certainly could not have remained in Verona without telling their families, They rushed into things without thinking, a decision that was bound to end in disaster, just as Friar Lawrence warns Romeo;
"Wisely and slow, they stumble that run fast." Act 2 Scene 3 Line 94
Rushing into marriage without planning or thinking of the future was never going to end well. In this sense, Romeo and Juliet can be held responsible for their own deaths.
However, we must remember that Shakespeare needed the pay to move quickly in order to ensure that he did not lose the audience's attention. If he were to include extra scenes with Romeo and Juliet getting to know each other or making plans, he risked losing his audience due to the lack of action on stage and slow progression of the plot. This is the same reason that Shakespeare has strong, romantic scenes written directly either side of conflicts, the juxtaposition of scenes; it captured the audience's attention and kept them interested and watching. If people began to leave during a performance because things were moving too slowly, Shakespeare would have lost his credibility