This ^^ I think the ONLY reason iphone users would be upset about this is because it takes one less argument out of the list of what makes ios better than android. Instagram no longer sets ios apart, as it can now be had on other platforms.
In a practical way - how could this be bad?? Or wrong?? Could you imagine if another major app were one-platform-only? Like if you could only get facebook on Android or something? And unless there's a financial incentive for the developers to remain apple-exclusive, why on earth WOULDN'T they want to gain access to the many millions of Android users out there? And from the user perspective, it also should be a good thing. I know that in my friend pool there are many who use Android as well as iPhone - so now you have access to all your Android friends. Unless you are so extreme in your apple prejudice that you only socialize with other ios people (and I'm sure some sad people are actually like that) - it's a good thing.