"Now when the people complained, it displeased the LORD . . . "
Sometimes God countenances the complaints of people; and sometimes He does not. What makes the difference? When David complains to God, (as he did in Ps. 55:2), it is a moan that is mixed with faith. When these people (above) murmured against God, it was all about fulfilling the lusts of their flesh.
God knows that we are weak, and that we--unlike Him--do not know all things, and cannot always maintain perfect composure in all conditions. With those churchmen who have faith, and who are willing (by grace) to persevere, no matter how hard things get--He (God) will hear their complaints. For those who only want their bellies filled, with no concern for their souls--the Lord has no regard for their contentions.
[Puritan quote of the day: "God is a tender Father, and He would have all the love of His children." --William Bridge, in "A Lifting Up for the Downcast"]