Carbonating beer is fine. I believe what was originally stated was the co2 charger, which seems to refer to the small steel chargers that simply dump co2 into a container. Products that use these are usually designed for those chargers (for example, a charger containing 8 grams. While not impossible to dump 16 grams of co2 into a plastic bottle it wasn't discussed in this thread about the pressure it would create and if the bottle was right for it.
Many people do force carbonate beer in plastic soda bottles, but a larger co2 tank can be used and set to a specific setting using a regulator. For example, I'd set the regulator at around 20 for beer, and 35 for water/soda but I can vary the amount. The chargers just dump all 8 grams in.