The graphic pretty much makes my argument.
The general idea behind utilitarianism is pretty simple, you should do the thing that results in the greatest overall good.
The problem and the criticism are simple — how do you know what’s going to end up producing the greatest overall good?
The answer isn’t easy — essentially, you need to use your previous experience to guess at what will increase happiness. Kind of unsatisfactory, doncha think?
It seems intuitively plausible that we should seek to create the best outcome for ourselves and others — but, with a pure consequentialist ethical theory you can end up trying to do something right and end up doing the opposite.
A perfect example happened at my place recently — I was washing clothes. My partner’s jeans were dirty and I put them in the wash — seems good, right — until he needed to go out of the apartment and only had wet pants… I tried to do the thing that would result in a good (clean jeans) and ended up making him go out with damp jeans… oops.
The example is also telling because we don’t always know how our actions are going to impact others. We could do something we’d appreciate others doing for us and end up doing something that makes their life more difficult…. so, good intentions can result in less than good consequences.