Permanent Residents who are in the US legally have followed all laws and proceedures in obtaining this status. This means hundred to thousands of dollars in fees, paying taxes and generally contributing to the country's infrastructure instead of 'mooching' off the system.
Twice in the last 10 years, illegal immigrants have been granted citizenship with little more than a slap on the wrist. As a permanent resident, this is little more than a slap in the face to the hundreds of thousands of people who want to immigrate to the US and abide by the laws and regulations set forth upon them by the Federal Government.
Those that have been in the country legally more than 5 years as a permanent resident have shown more loyalty and respect for the country in doing so than those who come illegally.