PSG has the best position, and they are lucky because they have Lionel Messi as one of their big strengths. Therefore, when there are problems, usually Lionel Messi will be included because maybe there are also many who don't like Lionel Messi's game and try to make his enthusiasm at PSG collapse by receiving a lot of pressure like that.
Of course, the PSG fans think Messi isn't giving enough/his best for the club like he does when he is on International duty with Argentina, or when he played for Barcelona, and imo i think the fans are well within their rights to think that way. When they signed Messi there was quite a lot of optimism around the club, the fans thought he was the final piece of the puzzle that could finally deliver the CL for them, but two consecutive seasons now and they've been eliminated in the RO16 stage.
Having said that, i don't think it was a good idea for the fans to boo Messi a couple of weeks ago anyway, that's not the best way to show their frustration, thus i think the Argentine world champion is going to leave PSG this summer, he does not feel loved over there and so it is better for both parties if he goes. Anyway PSG's problem isn't with a single player, it is with the entire team.
Messi is an amazing player and he proved it in Argentina and Barcelona but recently he cannot have a good performance in PSG and that's all because of not having to focus and not having a good atmosphere in the team, I think Messi will have a much better performance after the returns to Barcelona where the fans love him and he will have the respect he couldn't have in PSG.