If people do not have to be Catholic, or baptized with water, to get into Heaven, then why did missionaries once travel far and wide to try to convert the pagans. Why bother? Following this argument, it would be better to stay home because presenting pagans with the truth would place a great burden on their soul if they chose to reject the truth.
Myrna, the writings of a saint are not de fide and they do not equal the words of a Pope speaking on faith and morals. Besides, I don't have the original writings of St. Alphonsus and you probably don't either. Anything printed now could very easily be tampered with. Maybe he thought you didn't need baptism with water, or maybe he did think baptism with water was necessary to get to Heaven. We really don't know, and he isn't around to ask.
One thing to think about is why would a just, loving God consign an innocent infant to limbo for all eternity, because he or she wasn't baptized with water, but let someone well beyond the age of reason enter Heaven? This never made sense to me.