Killing animals is inevitable regardless of diet. Your plant based diet requires growing crops, but tilling soil and harvesting plants kills millions or billions of invertebrates. They are so small that they escape everyone’s attention, yet they are still animals killed to make your food.
Fishing and hunting kills animals too, of course. But it does not require literally uprooting an ecosystem.
Finally, a trolley has no moral agency either. That doesn’t mean nobody should interfere with it, or even destroy it if it threatens enough other lives.