In any "lifestyle" context, the foundation of a healthy home is the respect for personal boundaries. The bathroom is universally regarded as a "private space." Intentionally intruding on that space—especially for sexual gratification—is a violation of what sociologists call the "social contract" of the family.
Once privacy is breached, the domestic environment often shifts from a place of security to one of anxiety. Psychological Perspectives
From a psychological standpoint, the urge to watch someone in a private moment (voyeurism) coupled with self-gratification can stem from various places:
The bathroom is a sanctuary of steam and warm light. The tiles, cool underfoot, contrast with the gentle heat that rises from the showerhead, turning the air into a soft, misty veil. A faint scent of lavender soap drifts through the space, mingling with the faint perfume of fresh laundry. The world beyond the door is muted, a distant hum that fades away as the water begins its steady rhythm.