Leaven as a bad thing

A CCite wrote:

‘Leaven’ is consistently used throughout the scripture in a negative context, referring to something that is sinful, morally corrupt, false teaching, and hypocrisy, for instance:”

Actually, it’s not used consistently in that manner. One passage is enough to refute that old chestnut, but I will give you two.

Amo 4:5 And offer a sacrifice of thanksgiving with leaven, and proclaim [and] publish the free offerings: for this liketh you, O ye children of Israel, saith the Lord GOD.

Lev 23:17 Ye shall bring out of your habitations two wave loaves of two tenth deals: they shall be of fine flour; they shall be baken with leaven; [they are] the firstfruits unto the LORD.