Don’t get into a discussion about it. Hear what they have to say, and then say
“OK, I hear what you’re saying. No pressure, though. We’ll see.”
Then when you are asked to date some particular guy say, “No. He seems a nice enough guy, I’m sure he’ll make someone happy, but it doesn’t feel like the right situation. If the right situation comes up, I’ll know it when I see it.”
If they start pressuring you that you are* never* going to have the right situation come up, you can say, “I’m OK where I am. I have the luxury of waiting for someone to knock me over. That may not happen, true, but I’ll accept where that leads me.”
IOW, don’t reject their point of view, but stick to your right to steer by your own light.
Yes, you could point out that the world is full of widows who are just fine, thank you very much, but I think you’ll do better by just agreeing to hear them and then refusing to argue. That is the hardest position to make an assault on, and that sounds like what you’re looking for at present.