Can entry duplicates (or multiples) in etc/hosts do any damage? Can entry duplicates in etc/hosts do any damage?

For example:

##
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.

127.0.0.1       localhost
127.0.0.1       localhost
127.0.0.1       localhost

# and stuff like that throughout the file
No, having duplicates is not a problem. Since the file is read in order, the first matching result is read, and the rest of the file is ignored. Having exact duplicates has no effect.