Safety of the ship, no; ships are constantly being updated with newer and safer technologies (see
www.oasisoftheseas.com and click on "Expecting the Unexpected" for a little look at ways Oasis of the Seas (the world's current record-holder for size), has developed safety precautions to deal with the abnormally larger crowds.
Safety on land is a different issue altogether. Is it more dangerous to flood a remote island with a group of tens of thousands? Yes. More people means bigger crowds, more likely to push and shove or to create problems with the locals, both safety risks.
Do you think that it is practical to continue on the "bigger is better" mentality in the cruise industry?