I tend to agree. Trying to weld a hot thing to a cold thing never works well. The process is touchy and unreliable.
I think I may of replied to you before, but parts from my Solidoodle are very strong. The heat transfer from the extruder when printing at 0.3mm is more than enough to slightly melt the previous layer and fuse them. Printing at 0.1mm makes an almost seamless print. When printing with a heated bed, in an enclosed space the whole print is slightly tacky and soft. The prints do have a grain, and that is the weakest part, but you can design items with that in mind. If you are worried about printing something out of ABS/PLA that is going to fail due to stress, having it injection molded isn't going to increase the strength factor by enough margin to stop it breaking.
If A = B and B = C, then A = C, except where void or prohibited by law. -- Roy Santoro