First of all, Hamas is not all the Palestinians (or even a majority, for that matter). Second, what would you expect them to say after enduring the brutal operations of Cast Lead and Pillar of Defense? The event was a rally - meant to RALLY their base of support. Third, what Hamas says it wants to do and what it can do are two different things. The caustic rhetoric from Hamas will continue until Israel genuinely tries to engage with it. Only then is more 'mild' and pragmatic behavior to be expected from Hamas.
from the article: Hundreds of thousands mark Hamas' 25th anniversary in Gaza rally