Saying that a burglar forfeits their rights when they enter your home is obviously not true in a strict sense, but I don't think anyone thought it was. It's more about moral right than legal ones.
You do lose the reasonable expectation of being allowed to go about your business.
If you are walking in the park you have a right and reasonable expectation to be allowed to continue to do so without interference. If you walk into a bank you wouldn't expect to be treated as a bank robber, but assumed to be a customer with innocent intentions.
When you break into someone's house you lose that assumption and should expect to be treated as a criminal (which you are now) and a potential thief/rapist/murderer. The householder has no way to tell which you are yet, but you have ruled out innocence by breaking in.
You haven't so much lost the rights (I think someone pointed this out earlier) but rendered them inapplicable to your current situation.
MIFFLAW you say "if it turns out that there WAS fault on the part of the homeowner, will all those who are currently particularly vocal on this matter be coming back to admit, equally vocally, that they were wrong?"
About what? we are discussing the rights of a homeowner to defend himself. It could turn out that the homeowner was an illegal alien on the run from the law in the US for mass murder and that the guy who died was selling knives for £4.99 and the family forgot to mention this little sideline.
If so what would that prove? We are pointing out that homeowners do have the legal and moral right to defend themselves while you are saying cowardice is the best policy and that the rights of criminals outweigh everything else.
We will still be right and you will still be wrong.