I think that slight variations in flavour are acceptable in a craft beer, but that is not the same as variations on quality.
If one batch is slightly hopier or roastier, or dryer than a previous one, that is just natural variation and it gives me something to comment on. The taste varies a little, but it's all still good beer.
If it is a case of something being wrong with some beers, then that's a different story. Teething problems are inevitable, so new micros might have some quality variation and that is forgiveable. Once they are established and have their system down, letting a bad batch of beer go out the door would seem foolish to me.