As others have said, you can’t be too zealous for Christ. And I would add, it isn’t evangelists' zeal that turns people away, it is the lack of love. Love, expressed with zeal, attracts and transforms. But the mere desire to change others, expressed with zeal, repels and offends.
When evangelists show up on my doorstep on Saturday morning, they know nothing at all about me: my joys, my struggles, my relationships. They just want to convert me into them. This is, at best, annoying.
On the other hand, when a friend perceives that I’m struggling with problems, invites me to lunch and offers to pray with me, they truly want to help me and I know they love me. This can be transformative.
If you have Christian friends who are being zealous in the first sense, I suggest you lovingly pull them aside and express your concerns that their efforts are not only ineffective, but counter-effective. The key is to deal with them in love; if love doesn’t change them, stop trying and merely pray for them.