Amazon begs to differ:
It’s not for your lens but for your dog 
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I don’t use any.
I use my breath and a dry optic tissue paper. They are incredibly cheap, but don’t damage the coating or glass.
If there’s a stubborn spot that just won’t come off, I’ll use a drop of ROR. But that’s all.
All my lenses are in pristine condition.
That’s a safe approach (assuming there’s enough moisture to work with) but glass and coatings are very hard. I’ve found that usually if either is damaged, it’s a result of something really dumb or excessive done by a previous user (including poor storage that leads to age-related issues).
This topic comes up all the time in astronomy circles: telescope objectives, eyepiece lenses, even first-surface refector mirrors. Common sense should rule but even reasonably contemporary optics are generally pretty tough.
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Yes, they usually are. It’s either by some excessive physical wear (like a sand particle stuck somewhere) or a chemical additive that degraded the coatings. Or fungus, but that’s another story.
My father had an old Praktica lens that had my fingerprint ‘embossed’ on the coating. Probably sweat & oil degraded it over time and he didn’t clean it promptly.
Either way, I rarely have the need to clean the glass. Even the lens used for astrophotography that gets exposed for hours at once is spotless with normal care that I do.
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That’s the best “rule” – Don’t clean unless needed. A little dust is far better than a scratch or a sleek.
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Wow! That’s some pretty good searching skills! Where/how did you find it? I can’t even find the scewdriver I bought ten days ago! How old is that stuff?
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Dust is usually innocuous and can also be cleaned with a blower, so either cleaning or not cleaning it is fine.
But oils and greases can damage the coating if left there for a long time, even if the lens is not used, and careful lens cleaning is unlikely to scratch modern lenses.
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Interesting recent video on UV filters by Mark Wiemels:
He notes that when the lens has a UV filter on, he is more willing to clean it in the field (because if the UV filter gets scratched, who cares?), whereas without the UV filter, he would wait until being in a cleaner environment with more tools. I noticed the same.
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In his initial accident, if he had a filter, the filter would have shattered and the shards would have scratched the lens. If you bump your naked lens on something not too hard (furniture, body part), it will probably not make a mark. If there is a filter, you can break the filter (much thinner glass) and create shards that will scratch the lens.
I always have a LensPen in the bag, as well as a microfiber cloth, so the “you can clean the filter with your shirt” argument hasn’t got much value.
So we are back to the last argument, the problem with filters is flare and you still need a filter good enough to avoid flare, which isn’t going to be cheap, so probably not in the wipe-it-out-with-your-shirt category, or if you do that to the filter, you can also do that to the lens, that has the same kind of coating.
There is also a good deal of gear-fetishism afoot, a scratch on a lens isn’t the end of the world (unless you are talking about resale value). You can mask a visible scratch by filling it with black ink (to avoid stray reflections on its edges). Roger Cicala has some interesting pictures shot with a completely broken front lens
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If your camera doesn’t look like this, are you even a real photographer? /s
Jokes aside, I don’t think a (not too) dirty front element is really anything to worry about as most dust spots are from the rear element or sensor. It can almost always wait when on the field. The only thing I’d say should get cleaned straight away is water, and with water you can’t really blow or brush the already present dust aside, so a filter is a pro in those situations imo.
In his video he did show some thick cinema filters, and I’d guess those could take a the hit easily without breaking and scratching his front element. Maybe someone should start producing thick protective filters 
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I think you make a very important point, which may explain why people participating in this discussion have different preferences.
I take a lot of photos during hiking, where water + dust combos are pretty much inevitable. It is not that I am reckless with my camera, but making sure that the I get no gunk on the front (or any other part) is a fool’s errand given the circumstances I use it in.
Sometimes I do not have access to tap water for days, so even keeping my hands clean (after eating, touching plants which have some sticky stuff on them, etc) becomes difficult, and grease/gunk from my hand transfers to the camera. Given these conditions, I am much happier cleaning my filter in the field than waiting until I get home (which may be in a week or so) or trying to clean the front element in the field.
OTOH I can easily imagine a setup where someone goes shooting photos for an afternoon, in a relatively clean environment, and does cleaning at home on a clean and well-lit table, on demand. Under these circumstances, no filter would be necessary.
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No denying a filter can protect from spray or dust (though on these occasions I usually already have a CPL on the lens). However in the video his primary motive is shocks…
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I agree. I found the video interesting because of the systematic testing of lens filters (the most consistent setup I have seen so far), but I forgot to mention this.
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