Spaying / Neutering to Prevent Unwanted Litters

So, I normally read this sort of thing on the dog facebook pages that I belong to, about spaying early to prevent unwanted litters.  But then I've noticed, more frequently, people are asking this about chins.

Now, some people choose to only have one gender.  All males or all females.  In that case, it is literally impossible for there to be an oops litter, because the right parts can't possibly match up.  So, no oops litters there.

There are also people who choose to have some males and some females, without the intention of breeding.  Just turns out, they like the looks or personality of this one chin, and it happens to be a male, and then later, they like the looks and personality of this other chin, and it happens to be a female.  So, they have two separate cages and separate playtimes and all.  No breeding intentions.

Here's where it gets interesting sometimes.  Often those people, who don't want to breed, ask about getting one or both of the chins spayed or neutered.  I usually would then ask, are they wanting to house them together (as a reason for doing the surgery).  No, they just want to prevent unintentional litters.

I'm starting to think maybe people aren't sure how litters come about?  As long as the chins are kept apart, in separate cages, separate play times, no together-time... there's actually no way for babies to happen.  I've actually asked people, are the cages close together (as in, close enough to breed through the bars)?  Half the times, they're across the room from each other, or even in separate rooms (like, one in each kid's room).  Ok, so they couldn't breed through the cages if the cages aren't next to each other.  Then I ask, joint play times?  Or, is that the goal (when one is fixed)?  No, they don't think the chins would get along, so they don't want to let them out together. 

Ok, so...  maybe someone can explain this to me.  How are these chins supposed to magically breed, creating an oops litter, which spaying / neutering is going to prevent?

I honestly feel the same about the posts in the dog groups.  I just read a post in one of the dog facebook groups, where someone asked, what age is appropriate to spay a female.  Some people said 6 months, some said wait until the dog is older.  Then one person said, as young as possible, to prevent unwanted litters.  Now, I didn't respond because I didn't want to get into it, but... if you're not letting your dog run loose, unsupervised... no unwanted litters.  Alternatively, if you don't nave an opposite-sex un-fixed dog in the house that the female will be around when she's in heat... no unwanted litters.  Is this sort of thing that difficult to comprehend?  Maybe it's just me.