Why do you think it is unenforceable?
Maybe it is enforceable but it cannot be enforced fairly.
What if someone has a response that is POTM worthy, but two other people already replied? Do we leave it to the admins to decide which posts stay? Do they delete everything after the first two?
I am suggesting that we 'pander' to new members.
I think this is a bad idea. It will just encourage the type of poster that adds nothing to the discourse.
I also do not think that having 'stones' should be a requirement to post on this site.
If a person is unwilling or unable to adequately defend their posts then maybe they should reconsider posting initially. If there is dogpiling the person should have the wherewithal to look at their initial post and figure out why no one agrees with them.
I think that being able to learn is a far more important attribute. But dog-piling can put people's defences up and discourage them from learning.
That is their issue. I do not think the person we are talking about is going to be more likely to learn if they only have 2 responses. Rather I think limiting responses to 2 will reinforce their thinking. If a person gets defensive because they receive lots of criticism then they are probably not very open to learning in the first place.
Facts don't lie or have an agenda. Facts are just facts