As many have said, a neopenis is not indistinguishable from a penis, neither is a prosthetic. Can it get erect, ejaculate, produce sperm, send the same sensation to the owner? No. Even if it were indistinguishable, silicone injections are supposed to be indistinguishable from fat when injected under the skin. It's still not your actual fat or body.

As for most gay men in this thread saying yes, there are a couple things. First, there's this message from a mod:

Asking whether gay men will date or be attracted to transgender men is a frequently asked question here. These particular questions are sometimes met with hostility and invalidation from transphobes or even just from people who don't understand the trans community.

I feel like that would color the responses. Seeing messages like this, it would be much easier to simply say nothing than say you wouldn't. It isn't an anonymous poll.

On another level, this question is asking "would you try this out." It isn't "have you tried it and did you like it" or "could you see yourself being with someone long term if you could only have sex this way." I'm a straight woman and if there were a cis man I really liked without a penis (accident, cancer, whatever idk) I might give it a shot. But would that be actually satisfying in the long run? I want to believe it could be, like I want to believe that if my partner got cancer I would be the perfect partner and put my life on hold to treat him. It... doesn't always work out that way in real life.

I should look for this video again, but it's from a woman whose husband came out as trans. She was bisexual so everyone was like "cool! This will work out perfectly!" And I think she felt that way too at first, but over time she knew it wasn't the same. She seems like the kind of person who would have answered yes to a thread like this, but the reality was that it didn't work.