I agree it's not our job to police that (and I stand with what I said earlier: I don't think that the other comics a reader reads means much about one's own comic).
But I thought of it recently again for my own comic, and I guess, that there is kind of a blur sometimes between knowing your readership for legitimate reasons (knowing who you write for, who's your readership), and worrying unnecessarily about what else your readership reads.
I think it would be easier if one could entirely ignore what kind of readers one has, but it's not really possible.
Eg: recently, I asked advice about two different mature themes in my -generally pretty harmless- comic. Both times, I was reminded by forum users that my readership was 'mature' (mature for comic readers that is ), so it should not be too much of a problem. I knew that, but did not really think of it, because I'm not used yet to assess my readers like that. I didn't think, 'what's the proportion of younger readers' etc, but it is a valid question, and if I actually had a lot of young readers, I would not be upset, but that would be a problem.
Here, no blur: if I had younger readers, I would have the 'wrong' kind of readers, I may have had to adapt, but I would not be upset at them, nor wonder what else they read or if it means my comic is too juvenile etc. Nope. I would just think, my comic happens to also have an appeal to younger persons (it's a coming of age story, but with a bit of a nostalgic feeling, so it would make sense if it was having an appeal to both generations).
Now, other eg: in a few months, I'm going to start publishing a side comic with a m/m relationship.
I'm absolutely terrified to get the wrong readership, and I may be very, very tempted to check the subscription list of new readers and get completely paranoid.
That's because I saw so many comments on m/m relationships similar to mine where readers bring horrible BL tropes in, sometimes paired with the awkward, upset answer of the comic author. I don't know how I'm going to deal with that (bad, for sure..) if it happens to me, and here, there is a huge blur between legitimate concern (will I have the readership that correspond to my story) and overreaction (suspecting people to possibly write distasteful comments based on their subscription list etc). I will do my best to not check people's list, but I know that means I'm going to be worried at each update.