Is it true that even quality knives with wood handles can warp and be contaminated with bacteria?
Knives are very hard-worked tools in the kitchen, and need to be easy to clean and maintain.

At all quality levels, unless resin impregnated or otherwise treated, wood does not stand up well to harsh treatment, such as frequent trips through the dishwasher.  Even if washed by hand, you want to wash it and then dry it, so the water doesn't soak in and lead over time to cracking and warping, plus a rough, unpleasant feel in the hand as the fibers expand and separate.

As to sanitation, wooden handles are much akin to cutting boards.  If treated properly, it is not an issue.  You can even, occassionaly, use a mild bleach solution (followed by rinsing and drying) to sanitize them.

If treated with reasonable care, by handwashing and immediate drying, wooden handles will perform very well, and of course they are very attractive.

Still, on balance, wooden handles require more care than some of the resin, plastic, or metal handles.  Choosing among the options is about balancing the feel and beauty and maintenance to your needs and desires.  For me, personally, I choose the resin handles as they are very durable and low maintenance.