I just wonder at what point Hitchcock has earned enough trust from the fans to not get up in arms when he does stuff like this. He clearly has reasons he's doing this, and I don't think he has any illusions about which lines work better.
One could argue that the team knew they were trading Stewart for a few weeks, and didn't want to upset the chemistry of a 2nd or 3rd line, so they put him on the 1st line with Backes. That's a line that has consistently played well with Schwartz cycling on and off, injuries to Steen, etc. There is little worry that the top line is going to struggle to put it together, so it was a good place to keep Stewart while trying to get everyone else going. (Of course, you could also argue that it was to showcase Stewart, but I think there are additional considerations besides that.)
Blues are poised to go on a run and win the Central. Catching Anaheim is not out of the question, but I wouldn't bet on it. Pretty much as long as they stay ahead of Chicago and Colorado, I think the Blues are in a good position. I'd also like them to stay ahead of all the Eastern teams, so that a hypothetical SCF has the Blues with home ice.
These complaints are like the threads where people want to trade off all the depth to ice the best possible starting roster. It ignores the detriment of losing all depth. The line juggling (if we should call it that) is part of getting ready for the post-season. I suspect he'll keep tweaking for a bit and then the Blues will settle in by the playoffs.
Part of this is also timing the crescendo to get the Blues peaking at the right time. Things get more serious after the trade deadline. We're nearly there. (Its conceivable the team has another move planned that would shed light on the current line combos as well.)