I actually haven't seen anyone vote down a review because they didn't agree with the Pros/Cons (except for one person, but that's minor). People should not do that by any means, just for disagreeing.
Something not being waterproof is completely different than saying that it "isn't harness-compatible" when it's clear that the dildo does not have testicles or a base. My example was, it's like buying a teddy bear or stuffed animal and saying "It's not a shirt," or, "It isn't edible." Well, it's obviously not edible and cannot be worn as a shirt, it's a stuffed animal!
I understand what you mean by saying that things being listed as Pros also should be able to be listed as cons, but listing such a thing that's evident as a lack of feature is something that implies negative feelings, which shouldn't be done because the person knew before receiving the product that it isn't harness-compatible. Listing it as a pro means that it's "an extra plus." Listing it as a con means that the product is lacking, which it by no means is if the person was able to see that it was not harness compatible.
Being waterproof is not something that we can see with our eyes; we need to test it. Harness-compatibility is not something that needs to be tested, it's a given (unless of course, like some people wrote, it has a base that's too floppy/small and doesn't stand up well to harness use).
Sometimes, we list things as cons to draw attention to them, I agree. Like Rockin' with a Cock In said, how porous the material is, whether it's rechargeable, if batteries are included, some properties of the material. These are things that we cannot always see by the pictures, and we write them to draw attention to them (especially the porosity of the material, that's something great to add for people reading reviews who have no idea about sterilization and safer practices). As I already listed, you can see quite clearly whether a dildo is harness-compatible or not (unless someone really inexperienced knows nothing about harnesses and thinks that any dildo can stay in one).
Throughout the review, adding this as a negative is alright, though. Saying something along the lines of "since there isn't a base, I do not recommend it for anal play and it cannot be used in a harness, even though it's lovely and those would be great extra features!" But adding it as a Con draws too much attention. I would only ever add something like that as a Con if the case with the floppy/too small base happened, or if the pictures were angled and I could not tell by the pictures alone.
I talk too much! This is just my personal opinion of the whole thing. I am trying to understand why people would think otherwise, but I'm still not. If someone could explain to me better why adding that as a Con is alright, I would appreciate it. Thank you.