Again, not an apples to apples comparison. Pitching in the bullpen and starting are still both relatively the same thing: pitching. You don't necessarily have to "groom" a starting pitcher to pitch out of the bullpen. If you have a surplus of starting pitchers, it makes sense to use one of them in the bullpen, whether it be in the 8th as a set up guy, or in long relief. Starting pitchers can translate to the bullpen with relative ease.
However, not all position players are capable of simply playing another position. Some players translate to other positions, and some don't Joey Votto has the athletic ability to play LF. He's played in the minors. How well he plays it is still TBD, but he has played it before. All reports indicate that Alonso's transfer to the outfield would not be as smooth as moving JV to LF.
This move does not "send a bad message" IMO. If the Reds feel this is their best chance to compete, then I think they should do it. If it turns out that Alonso tears up AAA, Frazier/Heisey/Francisco/Gomes struggle/get injured, and the Reds need a bat, this is a legit option.
No one is saying Alonso is better than Votto. However, IMO, Alonso can only play first base. Joey CAN play other positions. Do I think that he should? Not necessarily, but the point is that he can, and there is a solid chance that the best Reds lineup includes JV in LF, and Alonso at first.