Why does it have to be one or the other, when we can do both? The other selling points of Ubuntu Touch don't magically go away just because it can also run android apps.
Having Android app compatibility helps lower the entry bar for many users. I'm not talking about the general public and people without any interest in Linux and free software, i'm talking about Linux users that still need (not because they want to use them, because they have to) certain apps, like WhatsApp, Snapchat, etc. Even some UBports team member even carry an iPhone or Android phone additionally to their Ubuntu Touch device with them in order to use these (not pointing fingers here). That is ridiculous, and if we can avoid that, why wouldn't we? Sure, you can dislike these apps, but if you need WhatsApp for your work, what are you going to do about it?
Another thing that is disregarded in my opinion is the open nature of this project. A (imho) unique selling point of Ubuntu Touch is the fact, that it let's you use your phone like a real computer. I'm not talking about attaching a screen, mouse and keyboard here, i'm talking about the open nature of the OS. You should be allowed to run whatever weird-ass piece of software you find, just like on the Linux desktop. And Anbox already works on the Linux desktop (in fact, it already works more or less on the phone as well), so artificially breaking compatibility would seem really weird to me. If i want to run something on my phone, who the f*ck are you to tell me not to do so?
The argument that Android compatibility would discourage developers from creating native apps for Ubuntu Touch is only valid up to a certain point. Big for-profit companies don't care about Ubuntu Touch, the market is way too small for that. There won't be a native Whatsapp client, there won't be a Netfilx app, that's just how it is. Again, you can go all Stallman about it and say that you don't want to use these services anyways (and you are probably right), but until there are alternatives, it is kind of necessary for many people.
What's also disregarded in the discussion about the unavailability of Google Mobile Services is how many apps work perfectly fine without them. 2300+ free and open source apps from f-droid change the math a lot. Also, many of the Apps from Google Play are available as Apk downloads, and can be used without Google Mobile Services.
Last but not least, i want to remind you a) how hard it is to develop Apps for Ubuntu Touch at the moment (ask @DanChapman, he will sing you a song about it) and b) how much work it is to maintain the SDK. UBports only has a very small and busy team, so having Android compatibility just takes the pressure of for now. It is by far not an ideal solution, but it could help a lot of people using Ubuntu Touch as a daily driver, and that's what we're aiming at after all. We don't want (and we won't) make Ubuntu Touch just another Android rom, we have unique advantages that won't go away. We will still have native apps. But having Android compatibility is the right decision for now.