[Siegmund]

To the OP:

You are far from the only person who finds this strange. I imagine almost everyone who makes the transition from online to B&M wonders the same thing.

The actual rule is crystal clear: "Any player who has been dealt in may request to see any hand that is eligible to participate in the showdown, even if the opponent's hand or the winning hand has been mucked."

The problem, as you discovered, is that there is an unwritten tradition of asking only if you suspect fishy business - which, in turn, means that if you exercise your legal right to see, your request will be viewed as a veiled accusation of cheating.

The rules include the absolutely useless further remark
"However, this is a privilege that may be revoked if abused." This presumably is there so that the defenders of tradition can prevent a custom of "all hands shown down get shown" ever taking hold. It doesn't offer any guidance at all about what constitutes 'abuse' of this privilege. In particular, "asking to see your opponent's hand every time he calls and mucks" does NOT appear on the list of improper actions that leads to warnings and worse in the etiquette section of Robert's Rules.

In short, the written rules and the unwritten rules are completely at odds with one another. No alternative, really, except to deal with it. If you are playing in a room where Robert's Rules are in effect and someone takes offence, you might ask the floorman to politely read the "any player may..." rule for the table - but he also will, most likely, politely tell you of his room's position on the unwritten rule and tell you whether or not your continued asking will be viewed as abusive.