"and that felons are protected from such by the 4th amendment."
One is not a felon until he has been convicted in a court of law.
I stole my own bicycle back from from some kid who parked it in front of a store. Everybody who saw it thought I stole HIS bike and were chasing me down the highway. Glad you weren't there, I'd likely be dead. ;-)
I profoundly disagree, one becomes a felon at precisely the moment that one commits a felony. Conviction or acquittal is a discovery or "finding" of guilt or innocence not an imposition. I do not think that LEO's and citizens should carry out the punishment of felons sans due process but I easily make a distinction between apprehension and punishment. "Innocent until proven guilty" is a matter of regard not a matter of treatment (suspects are arrested) nor a matter of fact (the guilty are guilty from the moment of offense).
BTW: You should not steal your bicycle back from the thief because you have deprived him of his due process. What if you made a mistake? You would then be a criminal! You should have reported him to proper authorities who would have recovered your property and hopefully apprehended, tried and convicted the criminal, resulting in justice for all. Have you never heard: "don't take the law into your own hands"?