Single worst decision in Blues history ... well, let's go through the list of contenders.
Yes, Mike Keenan is in here. Yes, his tenure was checkered. He also swung the deals that got us Pavol Demitra for Christer Olsson, and Chris Pronger for Brendan Shanahan (who, if anyone knows the backstory here - and I can't imagine anyone doesn't, as often as the main piece of it has been alluded to over time - Shanahan
had to be shipped out). Is his tenure all-in-all bad? Yes. Worst move ever by the team, though? No. Especially since he kept the Blues from having to wear
this all-time atrocity.
Yes, there's really bad trades over time. Adam Oates - though if he could have just shut his mouth and played out a contract, he wouldn't have been dealt. Doug Gilmour - yes, there were the rumors he'd molested a 15-year old. The return we got, though, was beyond dismal. Joey Mullen. Oof. Rod Brind'Amour, who got dealt because then-head coach Brian Sutter hated him. Chris Pronger. f***ing oof.
Yes, there was even missing the 1983 draft entirely - though for all the talk of who the Blues could have picked, they had long before traded their 1st and 2nd round picks so they weren't getting any of those guys, and then we're talking about
maybe they would have hit a home run with one of the later picks - something that, given their draft history to that point, seems really unlikely.
I might even mention tampering with Scott Stevens as an RFA, because (a) it was intentional, (b) all the evidence was sent to the NHL office and/or to Devils GM Lou Lamoriello, and (c) it cost the Blues a 1st-round pick, a swap of 1sts and $1.5 million
on top of the 5 1st-round picks the Blues had spent on Stevens back in 1990. Oh, and that whole "Shanahan for Stevens" thing, too.
My vote, though?
Bill Laurie owning the team. Laurie plucked the team with great fanfare in 1999 and set about trying to buy the Cup, joining the annual arms race in the West with Detroit, Colorado and Dallas. He also decided to go off on diversions like trying to buy an NBA team and move it to St. Louis - one of the worst kept secrets ever in the NBA. After ~6 years, having not won the Cup and the team trending down out of the top ranks of the Western Conference and with the league moving into the salary cap era, Laurie decided he was tired of losing money (which he didn't have an issue with in the years prior, where there was no salary cap) and turned into the sore loser who decides everyone must suffer, and announced he was selling the team But it wasn't just that. He decided to sell the team and trash it on the way out, unloading assets for cheap to make it "easier to sell" and "more attractive" for any potential buyer.
In his tenure as owner, he also allowed trusted lackey Dick Thomas to oversee the team in an unofficial capacity, and Thomas helped scuttle and/or orchestrate moves repeatedly with his interference. [See: not trading for Hasek, trading Pronger for relative pittance, et. al.] The Bill Laurie Reign of Terror set the franchise back several years and required a largely ground-up rebuild, and broke the trust of a number of Blues fans along the way.