Sad Exp.
You wrote:
Imagine. Boy B will learn how to stand up to bullies in his own time.
But if he's going to be bullied right from the start, he has no chance to develop himself. It's like a woman having a bad experience on her very first date or you being sacked 3 days after you get your very first job.
These are children- barely infants we're talking about. All that standing up stuff comes out as the child grows.
My response:
Children are growing from the moment of conception. At each stage in their development there are lessons to be learned. Some are tougher than others, but IMHO parents need to use every experience as an opportunity to teach some of those valuable lessons.
IMO, if you wait, the child gets the wrong message, and it will be hard to "unlearn" the subtle lessons taught at such an early age.
You also wrote:
That's how violence starts in the world because of this "tough love" sh!t. We all start carrying guns and belting people up 'cos that's the real world we live in.
My response:
WHOA!!! 
At best, this is a giant leap into maybespace. If you can prove (And I mean empirical evidence) your case, I will be happy to listen, but conjecture like this is too much for me to buy.
And regarding the following:
Original poster, don't listen to Imagine. Not at this juncture of your son's life.
My response:
I think that Imagine has done a very good job of summing up the options open to the original poster. 