Of course, I will not support someone in something I believe to be wrong or misguided, but I am far more likely in those cases to simply say nothing than to contradict them outright. On the basis, I think, that they are likely to know their own business better than I do, and that what seems alien to me may very well be the right thing for them.
At most, I will point out what I perceive to be significant flaws or holes in their proposals; but in the spirit of "how do you propose to deal with this problem as part of your plan?" or "perhaps you might want to revise this element", rather than as "this flaw shows that your plan will not work".
On the same lines, if someone says "From now on I am going to do x, y or z" and a few weeks later is no longer doing whatever it is, I will refrain from comment, assuming that the person concerned is already well aware of their failure and that mentioning it would simply be rubbing salt into a wound.
Essentially, I'm not sure whether I should be trying to change any of this. Obviously I don't want to (and probably can't) reverse direction entirely and become incredibly forthright and abrasive. But ought I try to challenge things I disagree with more strongly, or is my current 'softly softly' approach actually more effective?
Personally, I quite like being challenged and even provoked sometimes (and in such cases I will rise to the bait and become more combative than usual); but it has to be done in the right way, and I'm not sure I can even articulate what 'the right way' is ('a kind of respectful teasing' is probably the closest I can get), let alone be sure that I am following it if I start provoking others. Whether I like or dislike that sort of challenge also depends on my mood at the time - next to impossible to judge for situations like livejournal, and difficult enough even in person - and on nebulous things like the intentions behind my saying or writing whatever it is that's being challenged (for instance I'll often put forward ideas in a spirit of exploration, in which case I'll find it disconcerting for them to be challenged as if they were rigorously-considered assertions).