"Safe" for whom? This could mean several different things:

• Does eating (a particular) GMO food cause health problems?
• Does planting (a particular) GMO food crop cause chemical environmental problems, e.g. a chemical expressed by GMO crops causing beneficial insects to die off?
• Does planting (a particular) GMO food crop cause biological environmental problems, e.g. by becoming an invasive weed?
• Does planting (a particular) GMO food crop cause economic or governmental problems, e.g. by contaminating adjacent non-GMO fields with pollen from a patented gene line?
• If GMO crops are very successful in the market, will this lead to crop monocultures that will experience catastrophic failures?

As with "organic food", the halo/horns effect is strong with this one.