Yes
Now, I wasn't around on ICO or the forums when this game came out...but, since I started playing this game I have managed to get 7 of my friends to play this game, and I have one other who owned it before me...
That is 8 people I know personally who own this game and play it...I have played LAN games with all of them, so these people are not inherently opposed to MP...yet, not a single one of them plays on ICO...and the reason is, they don't want to get their butts kicked...
All of my friends (and I'd bet probably most people who bought this game) came from a background of strategy games...and most of those are grounded in SP, not MP...they are used to SP, they are used to an AI that they can always beat...playing against someone that can actually beat them is not something they are used to or comfortable with...
How is this related to smurfs?
You love sins, you are looking for an extra challenge, and you learn about ICO...you are finally willing to come out of your comfort zone and risk actually losing...you play a 1v1 against a guy who says he's a noob and isn't very experienced either...and then, he rushes you with 3 carrier caps and 20 LRFs and absolutely hands it to you...the thought of total humiliation hanging over your head is a huge reason to never play again...
When you can look at someone's stats and get a good feel for what level they are, you are then able to find players that are the same skill as you...you are willing to play 1v1s with people who aren't going to beat the crap out of you...you're willing to participate in a 5v5 because you know the teams will be balanced even if you're a noob and some players in there are pros...
But smurfs throw all that out the window...its hard enough for a lot of people who own this game to even accept the risk of losing to a human player...but if you can't even find players your same skill level, the fear in knowing you'll likely get humiliated by a pro is enough to prevent you from playing again...
The, shall we say, unpleasant communication of some players doesn't help either...
The people who play sins are strategy gamers, space genre gamers...these people are not switching from Halo 3 to Modern Warfare...these people are switching from GalCiv II to Sins...
Trash talking is fun on Halo 3...there is an understanding that no one really cares who wins...most people trash talk because it's funny...it is understood that it is not personal, not serious, and likely uncharacteristic of the person doing the trashing...it is simply part of the entertainment...
Sins is different...the most trash talking these strategy gamers ever get is a half insult from Emperor so and so when they open the diplomacy tab to trade a new technology...these people will take trash talking personally and/or be easily turned off by it...
Smurfs can get away with trash talking because of the anonymity...and therefore, they are more likely to trash talk...if people know certain players are jerks then those players become unpopular...when those players can simply smurf as Barney Killer or some other ridiculous name, and then do it again, and then do it again...it becomes a huge turn off...
Of the nine people I know personally who play this game (including me) I'm the only person who plays on ICO or has played MP with someone I did not know personally...I'm also the only person to have played a MP console game online...I really do believe there is a correlation...