Is saying something negative about a particular belief automatically considered "denigrating" to anyone who holds that belief?
It's almost always more productive to critique ideas, concepts, beliefs, etc., themselves rather than criticizing the people who hold them -- but what are you supposed to do when someone automatically takes personal offense at any negativity directed at their beliefs?
While I'm not going to go out of my way to insult and annoy people for the sake of insulting and annoying them, I'm not going to shut up and be quiet on every issue that I'm afraid might offend someone either.
As for effectiveness... it's very hard to ever change any one person's mind on anything no matter what strategy you try. If I could go from 0.01% chance of changing someone's mind to a 0.1% chance, by virtue of the most careful, cautious, diplomatic language I can muster -- it's hardly worth the effort. Not when there's another angle from which I can be far more effective with direct, even scathing language -- changing the entire atmosphere of public debate.
When atheists tiptoe around religion and treat it as a topic of special reverence, as something off-limits from criticism, as something automatically due some special kind of respect without any regard to the merit of particular beliefs, they work against their own interests. Acting like that isn't merely neutral, it boosts the position of religion in this world.
I predict that the new outspokenness of many atheists is very likely to have a measurable impact over time. You'll see more and more people openly and willingly declaring atheism, and it won't just be people who've been silent before, but new people who've left religion behind, and new people who've never adopted any religion (or "spiritualism" or other metaphysical superstitions) in the first place.
The way forward here is frank, honest, and sometimes scathing criticism of religion -- silence, excessive tiptoeing, aren't going to cut it.
Even if you believe they are obviously wrong it should be clear that they believe the things they do for strong reasons.
If by "strong" you mean "difficult to shake", or "emotionally charged", or "well-padded by ignorance", perhaps yes. But if you mean "good" -- I find it all to rare when people have good, solid, well-thought out reasons for the things they say they believe.