What?: Rogues get simple weapon proficiency.
Why?: Rogues get pretty much every simple weapon at their disposal, save for the sickle and spear. I feel that fits weirdly, both thematically and mechanically. I can't imagine giving them the starting feat would upset any careful balance. Especially since you can just take Martial Weapon Proficiency and skip having to take Simple Weapon Proficiency.
I absolutely agree. Monks too.
With their only good two hander taken from them (quarterstaff) , I think even at a balance point of view it would solve a problem.
rogue's being able to use Q-staff would be a dream come true
So, it's worth mentioning; rogues do get quarterstaff under rogue proficiency. The downside is that quarterstaff is considered a double weapon, so, you can't get a STR/half weapon, or a sickle to have a cool sickle weirdo aesthetic.
It's strange that sorcerers can use weapons that rogues can't!