"need" is a strong word.
But regardless, I'm more interested in why you think we'd be better off without one at any level. I don't see any point in haggling over the level until we've dealt with that. So in the interests of moving this debate along, I hereby rescind my previous comment and say that a level of $3/hour seems like a reasonable floor. An hour of man's time should certainly be worth at least that much, right?
No. $3/hr might be too high for some jobs.
But OK, I'll give you a pass here and go on to my argument.
Wages represent value of labor for the employer. Take a welder for example, which is pretty highly skilled work. But a welder isn't worth $5/hr to me because I dont run a welding shop. But for someone who does, his welder could allow him to make X many dollars in profit by employing him. If he's a good welder, he is worth more because he works more quickly with fewer mistakes. A bad welder, less money. But there is some limit to what the welder can be paid. As crucial as his job might be, it isn't worth $500/hr because paying him that much will cost all the profit the company makes. And what's the point of running the company in taht case? Also you could hire another welder for less. Or hire someone and send him to welding school for even less.
So there is a market level for a welder, because every shop that employs welders is competing for that welder's services.
Now, just like the welder, unskilled labor is also subject to a market, with many employers competing for unskilled labor. So there is a natural rate, a market rate, that unskilled labor commands.
If you set a min wage higher than that market rate, you eliminate all the jobs that would exist in its absence. It is not simply luck that you don't see gas jockeys or theater ushers anymore. In my childhood, 60's and early 70s, those jobs were always filled by either kids or retired people.
So the choice is not between jobs at $8/hr or jobs at $15/hr. It is a choice between jobs at 8/hr or no jobs at all. And if you look at teen unemployment rate (teenagers being the most likely to work min wage jobs) you find that in fact rises in teen unemployment virtually mirror rises in the min wage.
I would like to hire someone to sweep my floor in my little shop. If i could hire someone for $2/hr I would. Maybe no one wants to work for that wage. Maybe the retired guy next door is bored and would do it just to get out of the house and earn a little pocket money. W ith min wage laws he loses that choice. It isn't worth $10/hr for me to pay him to sweep out my shop. I'll do it myself for that amount. That is how jobs disappear.