Yep. For the $20+ they get paid in cash to watch the games along the touchlines, the ARs could at least do the bare minimum requirements of their jobs - stay with the 2nd-to-last defender, follow the ball to the goal line to confirm a goal/no-goal. And actually calling fouls right in front of them would be good, too.
as i pointed out before, very often parents like yourself, are misinformed or just plain don't know what they're talking about. as for $20 paid in cash..... some games are cash, some aren't. an AR does not make $20 per hour, especially when factoring in things like being at the field early, time between games, etc. etc. the referee team makes $1.50 per minute of game time, with the lion's share of that going to the center.
i'm not sure you know what you mean when you point out the "bare minimum" required by an AR. as for calling a foul directly in front of them.... is it a foul? or is it what the biased parent thinks is a foul against their team? is there an advantage that possibly is developing? if it is a foul, would stopping play make the game better? is the center referee looking right at it, and therefore even if the AR might have called a foul, he is allowing the center, who is ultimately in charge of the game, to make that decision?
my point being, you just might not know quite as much as you think when you try to critique someone's job, that you aren't trained for.
my advice: go watch your son or daughter play and enjoy the game. it isn't life or death no matter what level they play at. if you disagree with a call, get over it, and get back to enjoying the game. you aren't going to change the call no matter what you say or do. in the end, it's about kids playing soccer, not about parents obsessing over whether the referee's assistant is running hard enough to make them happy.