Understanding ものだ to make general statements


I'm trying to understand the use of ものだ to make generalised statements. I
think I failed to use it correctly in [this
sentence](https://japanese.stackexchange.com/questions/41457/how-to-say-ever-
in-this-context/41458#41458) (note that this question has a different emphasis
from the link).

I'll start with a use of ものだ which I know is correct, so you can understand
what I'm getting at:

> だれでも新しくて便利なものに興味を持つ **ものです**

Suppose I want to make the statement that cats are not friendly. Here are my
two attempts:

> A) 猫が人なつっこくない。  
>  B) 猫が人なつっこくない **ものだ** 。

What changes between A) and B)? Without further context if I say sentence A)
will the listener start looking around for the **particular** cat I'm talking
about? Or will they take it as a general statemement that I think **all** cats
are unfriendly?

Is sentence B correct? In the linked question I was told to use 生き物 (in a
different position) but I think that's because I was unclear in my question.




I feel a cat in sentence A is the particular cat. However I feel cats in
猫は人なつっこくない are all cats as a general statement.This is because of the
difference between は and が.

So I feel your sentence 2 is unnatural because ものだ means "something everyone
says generally". 猫は人なつっこくないものだ is natural. And you can use ものだ for creatures.
For example, 赤ちゃんは、よく泣くものだ(It is said generally that babies often cry).




I feel a cat in sentence A is the particular cat. However I feel cats in
猫は人なつっこくない are all cats as a general statement.This is because of the
difference between は and が.

So I feel your sentence 2 is unnatural because ものだ means "something everyone
says generally". 猫は人なつっこくないものだ is natural. And you can use ものだ for creatures.
For example, 赤ちゃんは、よく泣くものだ(It is said generally that babies often cry).

