​All the sacraments, as a general rule, should be celebrated in a sacred space. Therefore, a dedicated parish church or oratory is almost always the proper place for the celebration of any sacrament. 
 
But, as is almost always the case with general norms, there are exceptions. For example, in danger of death, baptisms are sometimes celebrated in the hospital. On account of urgency, or as the result of a pastoral moment, confessions are sometimes celebrated in settings other than the church. 
 
In the example you cite, no Church building exists to accommodate the three million who assembled in Rio. The use of the beach was actually a backup plan that had to be implemented when the large open field that had been designated was rendered soggy by pouring rains. 
 
Hence, for urgent pastoral reasons, many general norms can be adapted where necessary. 
 
Regarding weddings, certain permissions can be obtained for weddings to be celebrated outside of the sacred space. However, the reasons ought to be serious, not just because it would be more convenient or pleasing to someone in the wedding party. 
 
While permissions are sometimes granted, most dioceses resist granting these permissions too easily. Of all the Sacraments, the celebration of Holy Matrimony tends to be most influenced by secular trends. And many of these trends take the focus off Christ and the actual Sacrament that is being conferred. The emphasis too easily falls on dresses, flowers, food, and other social aspects. Moving weddings to beaches, backyards, reception halls and other such places, shifts the focus even further away from the Sacrament itself. It also tends to open the doors even further to certain passing trends, many of which are questionable, even frivolous or scandalous. 
 
Hence, the celebration of the Sacraments ought generally to take place in the parish church. For serious pastoral reasons, such as stated above, exceptions can be made. But weddings seldom present pastoral conundrums significant enough to warrant the movement of the Sacrament outside the church and, more problematically, shift the focus even further from where it should be.

​The catechism here references a quote from St. Athanasius, and also a clarification by St. Thomas Aquinas. It is true that Athanasius speaks boldly, as Saints often do! But as both St. Athanasius and St. Thomas were careful to do, distinctions are necessary. 
 
The exact quote from the catechism is For the Son of God became man so that we might become God. The only-begotten Son of God, wanting to make us sharers in his divinity, assumed our nature, so that he, made man, might make men gods. 
 
Note that the second sentence, a comment by Thomas on Athanasius’ statement, the word “gods” is not capitalized. And this is to make it clear, as Athanasius would agree, that we do not become a god as separate and distinct from the one, true God. But rather, that we “partake” or “participate” in the Divine nature. 
 
To partake, or participate comes from the Latin Word particeps, meaning to take up a part of something, but not the whole. Thus, though we come to share in aspects of the Divine nature, we do not do so in a way that is separate from being members of Christ’s Body, through baptism. We access this “share” in a part or aspect of divine life and nature only in union with Christ, only by entering into communion with Jesus at baptism, and thus receiving divine sonship.