No, they aren't.

Comcast doesn't give you a free TV or computer if you promise not to cancel for two years and pay more than folks who already have the device.

This, though, is correct. It is easy for "competitors" to collude against the consumer. For example, if AT&T raises prices in a way which is irrational unless Verizon does the same, Verizon and AT&T can collude to raise prices in their entire industry without any direct communication or signalling.

This is contradictory. If credit lets me buy the phone outright (and then save more than the cost of the phone on reduced service fees over two years), why would I need a subsidized phone or an installment plan?

Easy credit doesn't explain why people accept grossly higher costs for contract phones. Instead, it raises the question: why don't people use credit to amortize the up-front cost of the phone, and then save money on service fees?

Or as a person with a limited budget? I think a lot of people can basically afford to overpay, and maybe they know they're overpaying, but they think it's not worth their time to figure out a better option.

Which is the inverse of all private assets.

Just because you're smarter than the average consumer doesn't mean you understand the modern financial system (or double book accounting).

Also, "Chevy" gas and "Ford" gas contain different additives (wired vs. wireless) so they "aren't competitors" even though they basically sell the same products: cars and fuel.

Pretending not to be in competition with other firms in the essentially the same markets is another method for fixing prices.

It's not closed when you are using large quantities of fossil fuels and petrochemical inputs to grow the corn.

There are better feedstocks than corn, for reasons of both environmental impact and efficiency, which also don't drive up food prices in international and domestic markets.

We use tons of petrochemicals to grow corn.