Drawing a bit of a long bow, aren't you Spuds? If you have nothing else but the expedite ie. no plan B, then yes, you are setting yourself up for a fall.
If, however, you use it like Scott says (and the way I do), then what's the problem? If you can see that you have 2 approaching, and the current climb isn't going to work, ask to 'expedite', reassess, then either it will work or they go on a vector. Some guys like to set the vector up anyway (the belts and braces view), but personally I feel that increasing your workload (by vectoring) can be just as dangerous in busy environments. Asking for a specific climb rate has it's own set of problems, and I feel is no better or worse than the 'expedite'.
We are talking techniques, here, so this is just opinion.
edited to say that I agree wholeheartedly with vectorline (posted the same time)