Actually a 30k dump all at once at current prices would drop btc's price down to about $500.  While I agree with you that people would just buy back in and the price would eventually rebound... a drop of $300+ dollars in a matter of seconds is huge and would likely lead to some serious panic selling at first that would drive the price down further.

It's not true that the price would drop only a little if that many coins were unloaded on an exchange at once.