Wrong. I've traded, and seen people trade debit verticals (1x1s) at zero many times on a single ticket. This also belies any basic rates arbitrage like conversions, boxes, etc. I've done dozens of boxes at implied rates on European ops at up to 8x LIBOR. Stating it is "BS" abrogates ANY arbitrage, which is, BS.
Arbitrage and the trade examples you describe are by no means "riskless" as was prescribed in the OP. I've personally seen arbitrage trades - even basis trades in the interest rates and commodities, get completely blown out due to squeezes.