So can any technology or just about anything. Access to food, sanitation, electricity, social contact, etc. can be abused by controlling partners. Anything electronic could be abused. What might be helpful for one person could be abusive and intrusive for another. Because things can be abused doesn't mean they should not be used.And many illegitimate ones, also.
This is something that can be abused by controlling partners, or those with tendencies to behave like stalkers, or, intrusive authorities in the event of unfortunate court hearings when such evidence may be demanded as part of the court proceedings.
There is nothing automatic about the Apple Watch tracking sexual activity.