They can be dangerous, and I say this for a specific reason.
What they are doing in general is ok, because they are preaching the word and trying to bring people to Christ. Even though their theology is not perfect, it’s still good.
Except in one case. If they are a OSAS Christians, then they are extremely dangerous in my opinion. St. Paul writes, “For know and recognize this: no sexually immoral or impure or greedy person, who is an idolater, has an inheritance in the kingdom of the Messiah and of God. Let no one deceive you with empty arguments, for because of these things God’s wrath is coming on the disobedient.” Eph. 5:5-6
OSAS Christians today present these empty arguements. They aren’t encouraging people to sin by any means, and they’ll encourage people not to. BUT they are so strongly convicted that faith alone saves you once and for all that they will go out of their way to attack the idea that we have to abstain from sin. They speak so strongly that it doesn’t matter if you sin. I personally think that they are leading a lot of people to Hell. Here’s why.
If a person lives his life invincibly ignorant and never knows of the truth of Christ, but in general beleives in God and tries to be a good person, there’s a decent chance they may be saved. Then along come these Christians speaking of Christ as the ultimate savior. Joy! Then they teach you that you shouldn’t sin, but it doesn’t really matter. This leads people into a lot of situations where they are being tempted, and they know they shouldn’t do something (full knowledge), but they say, ‘well Jesus’ forgave me for this so it doesn’t matter,’ and they do it anyways (full will), so they commit a mortal sin. I think it’s extremely dangerous.
They teach that with that one time profession of faith, all your past sins are forgiven, but that all your future sins are forgiven too. I really think this leads a lot of people into mortal sin, and so it’s better off for people to stay Jewish or to stay as someone sincerely seeking God in their own way than to be converted to this particular theology.