I didn't say that they would be infringing on Apple, Inc's trademark and I don't think that. I only think that in disputed ownership, based on instagram's purpose of providing a communication platform, the rightful owner would be Apple, Inc, not someone who happened to register it first. And they have a way of determining who the rightful owner, to them, is. Clearly the definition of rightful owner isn't universal, nor is it 100% consistently determined, but a process can be made for determining it. Here's an example: https://newgtlds.icann.org/en/about/trademark-clearinghouse/...
Do you think people don’t understand why Instagram is doing this? We know why a [powerful] entity would help another powerful entity. We’re not happy about it. Why would we be okay with the process of determining being of such sheer elitism?