Do creatures with summoning sickness deal damage while blocking?
From the rulebook:


  Unlike other types of permanents, creatures enter the battlefield with “summoning sickness”: a creature can’t 
  attack, or use an ability that has {tap} in its cost, until it has started your turn on the battlefield under your control. 
  You can block with a creature or activate its other abilities no matter how long it’s been on the battlefield.


Blocking is not "attacking back". Blocking creatures deal damage normally, whether they have summoning sickness or not. Again, the rulebook:


  After all blockers are chosen, combat damage is assigned. 
  Each creature—both attackers and blockers—deals damage 
  equal to its power.
  
  • An attacking creature that isn’t blocked deals damage to the 
  player or planeswalker it’s attacking.
  
  • An attacking creature that is blocked deals damage to the 
  blocking creatures. If one of your attacking creatures is 
  blocked by multiple creatures, you decide how to divide 
  its combat damage among them. You must assign at least 
  enough damage to the first blocking creature in line to 
  destroy it before you can assign damage to the next one in 
  line, and so on.
  
  • A blocking creature deals damage to the attacker it’s blocking.