Upgrades are not just for software anymore. Humans are steadily gaining access to technologies that enhance our brains and bodies. But most Americans, says the Pew Research Center, see this as yet another way for the haves to get a leg up over the have-nots.

Scientists are already working on synthetic blood substitutes to boost strength and endurance, brain implants to improve concentration and information processing, and gene splicing techniques that hack the human genome with surgical precision. Most of these techniques are designed to prevent debilitating diseases. Eventually, they will allow us to redesign our genetic inheritance.

That doesn’t sit well with most Americans. The majority of U.S. adults would not want brain or blood enhancements (66% and 63%, respectively) for themselves or their children, while about one-third favored such procedures. Of the 4,726 people surveyed by Pew, most were “very” or “somewhat” worried about technology-enhanced humans, believing the negatives outweighed the benefits for society.

Enhancements were seen as likely to exacerbate the divide between the wealthy and the poor. More than 70% said inequality would increase as benefits from enhancement would go to the wealthy first, and humans with “enhancements” would feel superior to those without them. Silicon Valley technorati are already curious about where such improvements might lead, with PayPal co-founder Peter Thiel expressing interest in parabiosis, transfusing blood from someone younger to improve health and potentially reverse aging.

Resistance to human enhancement appears to follow religious lines. People high in religious commitment were the least likely to endorse enhancements (agreeing with the idea that it was “meddling with nature),” compared to the less religious who were “more inclined to see the potential use of these techniques as just the continuation of a centuries-old quest by humans to try to better themselves.”

The sentiment reflects Americans widespread distrust of GMOs, which half of Americans think are unsafe (13% are unsure) — despite scientific evidence showing they are safe. Opinions did not differ by race, ethnicity, educational level, income or age, although women were less supportive of enhancements.