You cannot and will not go online without running into bad people with bad intentions. We all know they exist in the world, and the internet is a way to interact with other human beings in a completely anonymous way. So of course, you are going to run into them. If you cant handle that then you should avoid the internet, or at least stick only to people you know and trust. But even with a Christian dating site, of course the wrong kinda people are gonna go there and do what they do, why wouldnt they? The world is a fallen place, it is a place of evil intentions and sin. It should be expected that you are going to encounter this in your life.
But yeah, I agree, and not just Christian websites, God can use any place or platform for His will. I have talked with Muslims online before, who were by no means friends of Christ, and even with them accusing Gods word of lies, there have been times where one came out and asked me a sincere question about Gods word. I totally believe that God can use these things to help others come to Him, and does just that.
Actually, in my old life I was a member of a large online community that was NOT friendly about God's word, and was a strong advocate for the lbgt lifestyle. I was on their side with that lifestyle, and supported it. But after God called me I went there to tell them what happened, and that I was leaving that life. And guess what, all of them were against me but one girl, who sent me a private message telling me that I inspired her, and she said she would pray for me and everything.
Of course, we should absolutely avoid people who live in sin when we can. But that doesnt mean that God is not working His will in these places, and He may use any of us for His will, too.
(sorry, long post : /)