Yes, the attitude is what is offensive
Very much so.
I'd make a more general point about the dangers of acting out of one's ego rather than out of the Will of God.
(I could rephrase that to cover situations that have nothing to do with religion and involve those who do not believe in God, as it seems to be one of those useful universal principles of life.)
The Buddha had this principle as part of the Four Noble Truths, in which He said (essentially) that the root of suffering is attachment.
Other religions, and even areligious philosophies, have recognized this principle in their own version.
And this is how it relates to people being threatened/offended by having the Gospel preached to them:
Is it the Gospel itself, or the person doing the preaching who's acting out of their own ego/attachment?
In my experience, it's the latter more than the former.
Now, I would say St. Paul certainly had a point in his letter to Corinth that goes beyond the "offensive delivery of message" problem, in that the Gospel can be a challenge and people may reject that challenge, even when the deliverer of that Message is not acting out of their own ego.
Frankly, I would be more than a bit suspicious of any religion or philosophy that didn't make some demands on me to improve myself.
And really, who among us really
enjoys finding out that we're wrong about something and need to shape up in some way?
Sometimes people will take up the challenge and sometimes they don't.
For the author of the OP I would say this as well: When you're talking to someone about the Gospel, it might be helpful to keep in mind that you are just that sower planting a seed. You may never live to see that seed sprout, but it might, whether you're there to see it or not. The important thing for you is to just pay attention to when it's planting season and try to avoid being attached to results.