Doesn't @valfisher's point about rights miss the part about shared respect? Shared kitchens do mean sharing smells, but some smells (like fish) can really take over a space and make it tough for others to relax there. It's less about being sensitive and more about not making your coworkers put up with a strong smell during their break.
Look, microwaving fish isn't a crime. Lots of people reheat cod or tuna casserole without issues. Shared kitchens mean sharing smells sometimes. If you're that sensitive, maybe eat in your car. People have a right to warm up their food without being called selfish.