Yes! (There's often a change made in both sides!)
No. (Nothing gets done and we always end up back on square one.)
Yes, if it can make people relate to each other. Debates between similar religions can lead to the formation of a consensus that can make members of these religions more open-minded toward the other religion. Debates between irreconcilable religions have higher risks of being unproductive, but even in disagreement, it is better to debate about religion than to make war because of it. And, in some cases, these debates may lead to conversion of one group to the other. But this should not be the only reason for the debate, except within a given religion itself (like when the Church Fathers debated within themselves over what constitutes orthodox teaching and what is heresy).
Blow off some steam by destroying a religious person in a debate. Sounds productive to me!
no ones opinions will change
Religious debates accomplish nothing.