The main reason is that there is a huge difference between pointless post-season matches and pointless mid-season matches. Minor injuries sustained post-season don't matter, whereas Arsenal losing four players following the England-France game, quite clearly does. The second reason is the principle of choice. For their own reasons (yes, financial ones) Arsenal have elected to play these high-profile, low-effort games. There is no choice regarding international friendlies. This is wrong: clubs pay huge wages to employ players and then see them legally taken away by another organisation (e.g. the Football Association) and returned unfit for work. Can you imagine that happening in any other industry?
There also seems to be a creeping consensus that, unlike the rest of the European Union, the football industry should select its employees on the basis of place of birth. The justification for this outrageous stance is usually that somehow "will help the international team". Even if it weren't morally and legally more than a bit dodgy, where is the evidence that it would achieve its aim? How did club sides full of people born in England help the national side in the 70s and 80s? Moreover, how would it help Wes Brown's development if he knew the only reason he got a game at Old Trafford was because he was born in England and Jaap Stam wasn't?
The common thread in these arguments is the so-called club-versus-country conundrum. To me there is no riddle: football is the clubs.