That's true for rheumatoid arthritis (which is genetic), but not for osteoarthritis. OA is generally a repitition injury response (though there's a genetic factor as well), so it can be caused by weightlifting (I actually have minor OA in my shoulder from years of this). However, as long as you're training intelligently, have good nutrition, etc., the risk and severity are relatively minor.
gibran, if your family has a history of RA, the best thing you can do is to strengthen your muscles now and keep up a healthy exercise regimen and diet throughout your life. Even if there's a history of RA in both sides of your family, you only have about a 30% chance of getting it. But if you do get it, being healthy will help to minimize its impact.
Btw, this info is coming from my wife, who at 32 has been dealing with RA for 5 years.