2000 Lexus ES 300 struts

Suspension problem
2000 Lexus ES 300 4 cyl Two Wheel Drive 102000 miles

I need to replace strut and strut mount on passenger front side. It is recommended that I replace both front struts at the same time even though the driver side does not need it. I am told that the car won't handle properly if both are not done at the same time. Is this true or just another way to charge me more money? We plan to sell the car and are trying to do minimum amount, but want the car to be safe. Thanks.