My answer probably won’t be complete, but maybe it will help a little. :o
My first response to someone who accuses the Church of being “too legalistic” is to point them to the Code of Canon Law. All in all, it is about as long as the shortest Harry Potter book (just over 300 pages). The Church has been around for 2000 years and all its laws fit into one little paperback. Even tiny villiages that have been around for 50 years have law books that dwarf the size of the Church’s law book. If the Catholic Church really was so legalistic, wouldn’t you expect their primary book of laws to be bigger?
Second, was God being “too legalistic” when He gave Israel the Ten Commandments? Not only that, also read through Leviticus and Deuteronomy. It was more than just those ten commandments. God was pretty specific in telling the Israelites exactly what to do. The Catholic Church’s laws look somewhat lax in comparison.
Finally, it isn’t simply about what must be done. The ten Commandments aren’t just some divine “Donnie don’t do” list. They are guidelines on how to live a happy life. So too, the Church’s urging for us to receive the sacraments are not just some arbitrary hoops that the pope wants us to jump through to get grace out of some divine pez dispenser. The Church is following the will of Christ Himself on how people can best get to heaven and live happy, full lives.
We follow the laws of the Church, particularly regarding the sacraments, because we know they were instituted by Jesus Himself for our benefit. How could we not do what Jesus wants us to do? Perhaps some receive the sacraments solely out of a sense of obligation and fear of hell, but the true motivation ought to be out of love for our Lord and the Church He instituted.