Assuming good intentions is the sort of principle that is generally appreciated but rarely applied. I would like to establish it here, because I plan to reference it in future posts. The general idea is that, unless there is no other possible explanation, you shouldn’t attribute malicious motives to someone.
Moving away from any subject that could offend anyone, I’ll give you an example from the Council of Trent in the mid-sixteenth century. By this point, liturgical music used in the Catholic mass had become almost unworkably complex. Polyphony and complex orchestration made it difficult to understand the words. Part of a canon recommended, but not officially adopted, at the Council of Trent reads:
But the entire manner of singing in musical modes should be calculated, not to afford vain delight to the ear, but so that the words may be comprehensible to all; and thus may the hearts of the listeners be caught up into the desire for celestial harmonies and contemplation of the joys of the blessed.
There were presumably two distinct camps on this issue: those who were in favor of complex polyphonic music, and those who were in favor of simple, straightforward music. This quote illustrates the view the latter had of the former: that they were attempting to turn the Mass into an entertainment event, perhaps even intentionally trying to obscure the words to avoid the conviction that hearing them would bring. It’s easy to guess the other side’s position about them: that they were stodgy, joyless old people, possibly using the traditional Mass as a way of keeping themselves in power.
Assuming good intentions would reveal different motivations. The most reasonable assumption is to believe that both parties are trying to use the Mass to glorify God, but they are simply emphasizing different parts of His character. The first emphasizes His complexity and glory, the second His sanctity and superhuman nature.
By assuming good intentions, you can easily pick out most straw men. Straw man arguments, especially when allied with ad hominem, often rely on assuming that the opponent has bad motives: being completely self-serving, for example (as philosophical egoists decry acts of charity as being motivated by the happiness one gets from committing a charitable act).
One of the few exceptions, where I don’t recommend the assumption of good intentions, is when someone else has refused to do so for his or her opponents. If you don’t give it, you don’t get it, and besides, if you aren’t willing to believe someone else has good motives, what does that say about your own?