Swisslover is right about portions vs US. Starter portions are also very often on offer for main course dishes. And look at it this way. You are asking for the service for 2 people, the table for 2 people, the ingredients/cooking for one person and the bill for one person. Food is a small part of the bill in Switzerland so most restaurants won't be thrilled by this approach.
Can you do it? I would expect some to be OK, some to be annoyed, a small proportion to refuse (the de facto minimum charge). If that is really your appetite, and you hate to waste food, judge the situation when you see it Explain nicely that you are not so hungry and would it be OK....? The more formal the restaurant, the less acceptable and the more likely they will offer starter portions at 75% of the cost. Where starter portions are available, expect to order that rather than splitting.
Sharing desert is - of course - normal everywhere!