An anonymous commenter on Sentencing Law & Policy succinctly states why Lafler is a disaster:

Lafler is potentially revolutionary in that the State is now entirely at the mercy of defense counsel when it offers a plea.

Prior to Laffler, a competent prosecutor could try a clean case and present sufficiently solid evidence that any minor mistake by the trial judge would be a harmless error. Equally, by presenting an overwhelming case at trial, the prosecutor could try to make a solid case that any incompetence by trial counsel would not be prejudicial.

Under Laffler, however, that overwhelming case which defeats at trial ineffectiveness now helps prove that counsel was incompetent in advising his client to go to trial. I think most prosecutors could have lived with ineffectiveness limited to failure to advise -- that a prosecutor can cure on the record prior to a plea expiring, but including misdavising is open season for attorneys opting to fall on the sword for their client which is not as infrequent as the Kennedy opinion assumes.