Why is being a Dragon Slayer a big deal? Spoilers

During the story arc where Laxus is putting on his "entertainment" for the festival, it is revealed that...


   He is a Dragon Slayer


After this Natsu and others seem to be more worried about him.  Maybe it is just me, but it seemed similar to Goku going Super Saiyan or something.

Why does being a Dragon Slayer seem to make the situation worse?
You are asking two questions. Number one is...


  Why is being a Dragon Slayer a big deal?


And Number Two is...


  Why does being a Dragon Slayer seem to make the situation worse?


Dragon Slayers are a unique type of people who utilize a form of Lost Magic, Dragon Slayer Magic. It was a big deal that Laxus was a dragon slayer because...


  It is uncommon for someone to utilise a lost magic or to be a Dragon Slayer and for Natsu it could have been a perfect opportunity to ask if he had been raised by a dragon and if he knew where Igneel was.


Your other question however why does a dragon slayer seem to make a situation worse. I am going to answer this question based on the Fighting Festival Arc. I am not sure what you mean but ill tack a guess at this...

Dragon Slayers did not make the situation worse, they simply could not help due to Frieds Jutsu Shiki which prevented Natsu, Gajeel and The Master from participating in the carnival and freeing the girls who were turned to stone by Ever Green.