While I broadly agree with you, I think the post you're responding to has a point. You can't, in general, get a value back out of a monad, so if you call a monadic function, you may well have to return a monad. The obvious example is IO: there's no (safe) way get the `a` from `IO a`, so IO is kinda contagious.
Then again, there are lots of monads, such as `Maybe` and `List`, where you can get values out. These aren't contagious at all.
I agree with you that this is a good thing. Effects show up in the type signature - and it's all about those effects and managing them.
I think that applicatives and monads feel more contagious than they really are, because at first people tend to write functions that consume values of type `f a` too readily. This is because it takes some time to become comfortable with `fmap` and friends, so the new Haskell programmer often doesn't write as many pure functions.
Then again, there are lots of monads, such as `Maybe` and `List`, where you can get values out. These aren't contagious at all.
I agree with you that this is a good thing. Effects show up in the type signature - and it's all about those effects and managing them.