If you bump the lens right square in the filter hard enough, it may shatter and cause damage to the front element. But overall, it's not likely. What you get protection from is fingerprints and dust. It's much easier to clean the filter than the lens.
Agreed
Oh please. It is not easier to clean the filter than it is to clean the lens itself. They are the same task.
Any filter that only costs $5 is a CPOS (Cheap Piece Of Sh!t) and will ceertainly degrade image quality.
To ensure image quality is not degraded you need to buy quality, coated filters that cost many times more than $5. Consequently, the filter has the same cleaning issues as the lens itself.
Besides, how often do you clean a lens front element and what do you clean it with, sandpaper?
I get dust off my lens with a nice, soft, natural bristle brush and a blower.
Something like:
General Brand Large Rubber Blower Brush NP10093 - B&H Photo
As mentioned the shards of sharp glass from a shattered 'protective' filter usually damage the very lens it was intended to 'protect', since most blows that will shatter the thin filter are going to be towards what the filter was intended to 'protect', the front lens element.
Further damage usually results when the shattered shards scrape radially along the front of the lens when the destroyed filter is unscrewed, adding to the damage.
Thinking you are safe, could well mean you wind up being sorry you had a 'protective' filter on your lens.