Because :
Paypal is NOT FDIC insured.
http://forums.ebay.com/db2/thread.jspa?threadID=520029164&tstart=0&mod=1223732491372
When charge back happens, paypal will freeze your account money. That's bad.
About 解冻
I never do that, once it get locked up, I will open another one. I do not trust paypal with money, why I trust them with my identity?
Just holding some different paypal accounts will be much easier.