Read the fine print. You don't have any real rights to your permanent residency. The USA can decide not to renew it for any reason they deem fit.
Also, laws may change in the future that further restrict the entitlements permanent residents have. Permanent residents can be deported. I've been subject to extra screening in customs.
There's a lot of reasons to be a US citizen if you're planning on staying in this country for life.
Why? For what benefit? I haven't seen a reason yet to even consider doing that.