[xenihn]

Why are you bringing up the question of if it's illegal or not when no one else is? There's no dispute as to whether or not it's illegal -- it isn't. There's no argument there. There's realistically, nothing to be afraid of from a legal standpoint, which is what makes the behavior from organizations with large legal resources so puzzling.

People keep bringing up Facebook/Instagram and Snapchat. Facebook/Instagram has had no issue with admitting that Snapchat was an inspiration, so that doesn't help your argument. The issue here is credit and attribution, not legality or morality.