While the chemicals aren't necessarily bad, they can be very dangerous if used improperly, so use them carefully and in strict accordance with the manufacturers' instructions. However, no matter how many of these products you use or how often you use them, you'll never get rid of all the weeds. Their presence is not only inevitable, but desirable, as well.
Weeds give a lawn diversity, thereby enabling it to combat a number of pest and disease problems.
Weeds provide food and nesting sites for beneficial insects, and in some cases, weeds can actually enrich the soil.