This thread title made me very angry - it's Canon fanboys like OP that drive the insane Canon glass prices up. 3rd party lenses can be just as good as Canon's at fraction of the cost. Don't blindly recommend Canon's glass against Sigma, Tamron, Tokina, Samyang etc. - they all have some outstanding products, while having to reverse-engineer the AF communication.
The flip side is to get angry at Sigma, etc. fanboys for not being picky enough. This keeps the QC of the Sigma, etc., low; and allows Canon to keep high prices!
I hear both sides of this debate. Canon does prey on our wallets, but they've done that from the high ground of providing an all-around high quality product. Sigma has only starting providing such quality recently.
Sigma's only value proposition can't just be 'same as Canon for less money' because discerning professionals will see exactly how
3rd party lenses saved that money. In many cases, things other than the brute force metrics of sharpness and widest aperture are sacrificed to keep those lenses cheaper than Canon.
Remember that for a very long time, Sigma had quality issues: paint peeling, AF issues, odd copy to copy variation, etc. I am not a fanboy saying this -- Bryan Carnathan and Roger Cicala were saying this based on using, tearing down and repairing a ton of their products.
That said, Sigma is starting to move past being a 2nd-tier manufacturer and is finally making products that out-perform the Canon lenses. I cannot say enough how a single
lens -- the new 35 prime -- is changing people's opinion of Sigma.
So Sigma getting better is a problem for Canon but a gift for us. Here's to seeing more lenses like that 35 prime.