I think that most people you know do not recall what it was like when Reagan's amnesty was passed so it's probably nothing to to with that. But I think the problem is the declining quality of life in the US while we continue to support people who come here with no intention of being legal citizens. It's kind of an insult when someone has their hand out but can't even oblige even simple requests. There is a long list of the downfalls to being swamped with 20,30,40 million illegal immigrants so that list could provide some insight into why people do not want amnesty. I think the most obvious though is that, why should we reward one nationality for criminal behaviour? It's disgusting when you hear about good honest people being sent back to their homelands because of simple visa problems meanwhile we bend over backwards to cater to people come from Mexico that offer nothing more than to drag down the wages of the lowest paid workers already in the US.
I think it would be racist to allow 30 million people here from Mexico knowingly against the law to get away with breaking the law while we do not allow our own citizens to get away with breaking laws. That is practicing preferential treatment which is the same as racism.