Free national healthcare for everyone is a major advantage, especially for poorer people. When done right, that is.
Sadly the health system here is in shambles. It's considered one of the worst in Europe. They claim there's not enough funding, but I always question on how healthcare was actually BETTER back when Ireland was much poorer.
The people who complain about the NHS seem to be the type that whinge and moan... about everything. Frankly I find the NHS to be brilliant compared to the healtcare system here, and people like my uncle vouch on it.
As for Americans being against this, I frankly find it a bit stupid. It's for everyone, it's free and you would be soon thanking that you don't have to empty your entire savings in hospital bills.