Q: I need to replace the lower control arm on the driver side. Should I replace the passenger side as well?

Good question...generally, the decision rule when it comes to car parts, is "test, diagnose, measure and confirm" before you needlessly spend money replacing a part that might very well be perfectly good. That advice though does NOT apply to wear-out items such as spark plugs and the like. There, the rule is obviously throw away the part(s) automatically after "x" number of miles. Although it is possible to test the passenger side control arm, and verify its condition, you know it already has 180,000 miles on it. That is a lot of miles, it probably is worn, and so it would not be "unreasonable" to just simply replace it, particularly when you consider that the vehicle will have to be aligned after the driver side arm is replaced (it’s impossible to PROPERLY align a car with worn parts). So, hyper-technically, although you do have the option of inspecting the passenger side arm to see if it is still serviceable, I probably would replace it. Additionally, and getting back to the issue of the necessity of a good post-repair alignment, while you are doing this work you have to evaluate the condition of the other suspension parts, such as the tie rod ends, bushings and so forth. Any wear in the front suspension, in excess of what is allowed and specified in the Factory Service Manual will make it quite literally impossible to align the car to preferred factory specs. If you desire, a certified mechanic from YourMechanic can both replace the control arms and during that procedure inspect the rest of the suspension for you to see if there are any other issues that need to be addressed.