Tire Sidewall problems of the 2002 Nissan Sentra

In Mar '02, I bought a new Nissan Sentra se-r that came w/ firestone firehawk gta-02 195/55/r16 tires. I always rotate my tires every 2 oil changes (~7000 miles) and check/inflate tire psi every few months. In Jan 05 I went to allied tires for an alignment. When I picked up my car, they showed me large splits/cracks all around the inner sidewall of all 4 tires. (at this point my car had ~28000 miles) they said if I didn't get the tires replaced ASAP, I would have a blowout. None of them had ever seen anything like this. I had all 4 tires replaced at sears soon after. (it was est. 10000 miles of tread left on the "faulty" tires) the mechanic said he also noticed the splitting on the "faulty" tires and hadn't seen anything like it either. On may 31, 05, I took the "faulty" tires (which I still have) to Nissan. They didn't know what could have caused the splitting, and said to deal w/ firestone. At firestone, the mechanic said it looked like I got a bad batch of tires with the car, but that his comment was "off the record" since he didn't want to bad mouth firestone. When the manager came out, he blatantly beat around the bush, saying that since the tires weren't on the car, they didn't know if I was telling the truth (since the tires were off, he thought I could have purposely damaged the tires to take advantage of him, even though I had 3 other companies as eye witnesses). He then said if I had the tires still on the car, he would've been able to give me a pro-rated reimbursement. I still don't understand why the tires needed to be on the car for the manager to notice the fault in them. . . In the end, I was offered no compensation for these faulty tires, but the more important problem in my eyes is that of safety. I don't believe these tires are safe, esp. Considering my experience w/ them. For tires to "split" as mine did makes everyday driving for me and others around me very dangerous. I can send pictures via email if desired. Thanks for your time.