You CAN rip on a Radial... but not always with complete safety !!.. With a (new) sharp blade you are probably ok...

.... but what can happen is the top metal arm , although it seems sooooo solid, can bend just a little, the blade pops up to the top of the piece, and with its teeth, "runs" along the wood... all in a quarter second.

I was ripping a strip off a two by six, and this happened to me . The heavy piece of wood shot 15 feet across the room, and thudded into the concrete wall. When I retrieved it, the top surface had this neat row of teeth marks , right to the end. It happened faster than I could react.... and this was a very heavy board.

Fortunately, its pretty hard to stand at the "exit" of a radial saw set up for ripping, because its at the left side, , but it could grab your hand , and haul it into the teeth, as it was shooting the board across the room.

I have done all ripping since on a table saw ( which can also throw stuff at you, if you relax just for a second )

Be aware that the most dangerous tool in most shops is the saw., and use feather boards, kickback pawls, and extreme care.