Yes, they do.

This is the old camera-shop method -- sell a customer a lens, and then add considerably to the bottom line by also selling them a cheap filter for an inflated price. Just like 95% pure profit "extended warranties" are what keep many automobile dealerships (as well as electronics shops) afloat.

The problem with filters can be summed up like this:

1. If you have a cheap lens, they're probably not worthwhile. Just take the risk on the lens, and replace it if you scratch it badly enough.

2. For expensive or rare lenses, some form of protection could be a good idea if you are a klutz like me. But if you cover that nice expensive coated glass with a filter, you're basically crippling it.

There are several problems with filters.

3. Being of non-zero thickness, they cannot help but distort the light passing through them. None of the other elements inside that expensive lens are flat planes for that very reason.

4. The filters the camera shop pushes on most folk, have poor or non existent anti-reflective coatings, so the light is going to bounce around a bit too much. This can be mostly overcome by buying really expensive filters, in the 100-200 currency unit range. But again.. at that price level, it's probably cheaper to just go without, and pay for repair in the unlikely event that you ever scratch the lens. And there's the much more real risk of scratching the out-front 100-200 currency unit filter.. doh!

5. Since the filter sits out at the end of the lens barrel, it attracts flare from any point light source in the vicinity. It also reflects, or blocks, some of the light that would be better allowed to reach the camera sensor.

I put moderately expensive filters on many of my lenses when new. Most of those have long since been removed, in favour of lens hoods. These provide fantastic physical protection for the lens, don't block any of the important light rays, and reduce flare, ghosting, and improve contrast. But they do make some lenses more unwieldly and more obvious.

I still carry a few filters, for when they are actually needed for their original purpose: UV for very hazy sunlight, and polarizers for wet/bright conditions where I may want the sky to look blue (instead of white), or want deeper saturation on foliage and the like.

Cheers