Learn Italian: Visto che è socievole, non protegge la propria riservatezza. - Seeing that he is sociable, he does not protect his own privacy.

When the subject of the sentence owns the object, you can use a form of proprio instead of suo or sua to mean "one's own". Here, the subject "he" is the owner of the privacy, so propria is used to emphasize that he doesn't protect his own privacy.

Why does propria end in -a if the subject "he" is masculine?

Like all possessive adjectives in Italian, proprio agrees in gender and number with the thing being owned, not the owner. Since riservatezza (privacy) is a feminine singular noun, you must use propria.

Does the phrase visto che ever require the subjunctive mood?

No. Visto che (seeing that or given that) is used to state a real, objective cause or reason. Because it states a fact rather than an opinion, emotion, or doubt, it is always followed by the normal indicative mood, which is why we use è here.

If the sentence was about a woman, would socievole change to socievola?