The eighteen persons necessary for the performance of sacrifice are transitory and not permanent and karma in its nature inferior, has been stated as resting upon these. Those ignorant persons who delight in this, as leading to bliss, again fall into decay and death. (Mundaka Upanishad 1.2.7)
The ignorant following the diverse ways of ignorance, flatter themselves that their objects have been accomplished. As these followers of karma do not learn the truth owing to their desire, they grow miserable and after the fruits of their karma are consumed, fall from Heaven. These ignorant men regarding sacrificial and charitable acts as most important, do not know any other help to bliss; having enjoyed in the heights of Heaven the abode of pleasures, they enter again into this or even inferior world. (Mundaka Upanishad 1.2.9-10)
All these verse are against ritualistic part of the Vedas(strictly against)
What is Mimamsa's interpretation of these verses?
This verse from the gita says the same :
[BG 2:42] : Men of small knowledge are very much attached to the flowery words of the Vedas, which recommend various fruitive activities for elevation to heavenly planets, resultant good birth, power, and so forth. Being desirous of sense gratification and opulent life, they say that there is nothing more than this.