I wouldn't take issue with the U-3 measure if it was named in an honest way. A demographer or other statistician can certainly make good use of any one (or all) of the six measures.
The reality is that even a moderately educated person would probably assume that an "official unemployment rate" might describe the percentage of people who are unemployed, not some arbitrary function of that number. Maybe this is a carry-over from a time where the two used to be nearly identical. As of today, one rate is basically double the other. I view that as misleading, especially from a government agency whose sole responsibility is to calculate and communicate statistics about its workers.
If the government called U-3 the official "employment-seeking rate," it would be accurate, and the media would follow suit, and could still reference it without drawing my ire.
Maybe so but can you still not use whatever measurement you want so long as it is consistently done in order to get a gauge of growth or depression? It's not going to give you hard, true numbers but then again, neither does percent unless you know everything that went into making up the whole. After all, percent isn't a number, it's a ratio that just represents a calculation of two numbers. 50% of 4 is two and 50% of 20 is 10 and while I can certainly eat 2 cookies, I might struggle with 10.