When refereeing a paper, I often have objections to the work that do not rise to the level of using the coercive powers of a referee to delay or reject the work. For instance, I find myself wanting to write: "If I were you, I would be embarrassed to publish a paper with [such unclear writing/such a silly comparison to experiment/so few parameters studied/incredibly ugly figures]."*
If the paper is not wrong or incoherent, just lazy or badly written, I don't feel justified in rejecting the paper or requiring a revision. I also don't want to invest hours of time acting as a language editor or graphic designer for figures.
Is there a politer way to express this sentiment and encourage the authors to improve their own work? Or should I simply take on good faith that the authors have done the work to the standards they are willing to publish, and that these may differ from my own?
*note: this is distinct from the case where the paper is so unclear that you can't tell whether their work is correct or not - where I think rejection is appropriate. I'm also assuming that this is not a terribly selective journal - in fact, it could be a journal like PLOS ONE, which explicitly says that importance to the field is not a relevant criterion.
Note: I've edited this to address a couple of points made by answers, and to focus away from the writing part, which has been answered in the past. Bad writing is one aspect of this question, but general author laziness is the larger one.