Regarding Monchi, it's still too early to take a side since one never knows what will happen till the end of the summer transfer window, and the window hasn't even started yet. Even if Monchi leaves, it is well known why he would eventually do that (the things you are mentioning... issues with the board etc.)
Every Sevillista dreams of a stronger Sevilla, or a Sevilla that always makes steps forward. By selling 3-4 key players each year and experimenting with different replacements that sometimes blow up and sometimes suck badly... is not something that a serious team does. If a team wants to be consistently in the top 4 in the league and aim for more than 1/8ths of the final in the CL, it has to become a serious team, and that isn't done in the way that Sevilla was ran in the last years, with the board's decisions being the culprit for all of this.
Anyway, regarding the traitor thing... it's a personal opinion. The majority of Sevillistas (including me), do not treat players as traitors if they leave the club in a normal way, like most of the transfers happen. There was the weird case of Fazio where he even went to pay a percentage of the release clause himself just so he can go to Tottenham... he then came back and sucked badly, and he never had the warm welcoming at RSP, as many considered him a traitor. That was a special case as he left Sevilla in the final day of the transfer window, without much to do to replace him, and he was in top form back then (also the team's captain).
Another case of someone to be called a traitor would be if they join Betis (which as long as I remember never happened). That would be an inexcusable act, which carries a burden of guilt in itself.
As for the other players, including Rakitic, everything was normal and they possess huge respect within Sevillistas. Furthermore, the case of Dani Alves was quite interesting, where he was about to leave for Chelsea after the 2006-07 season, but in honor of the deceased Antonio Puerta and for the sake of the fans, he played for another year before going to Barca. How can you not respect someone like him? I guess that "fan" that you're referring to would also think of Alves as a traitor... wouldn't be surprised if that's true.