The argument will be that we think Malmo is an easy game to boost his confidence because long term we think Szczesny is a better option than Perin if both are at their normal levels.
However, given that Szczesny is making costly mistakes for club and country and we can't beat Empoli at home, there is no guarantee we will beat Malmo or that he doesn't make another mistake.
I think Szczesny is a lost cause at the moment. Let him fix his head on the training ground, the pressure is too much on him already without having to prove himself after making mistakes. Perin is not a world beater but had a fine season at Genoa and I wouldn't expect him to make these mistakes.