I only intended to comment on the altcoins that are known scams, but draw investors anyway.

Imagine you started XorNotBux, announced you were planning to sell a billion of them in a few months, then inflated the price with a much smaller supply in circulation. Some people will buy this (and possibly profit) fully knowing that you plan to obliterate it in the near future.

False. They do not all have the same structure as Bitcoin. Many of them are explicitly structured as pyramid schemes (premining, instamining, stealth launches, closed source launches).

While very few have unique selling points over Bitcoin, it is dangerous to assume they are 'at least as useful' as Bitcoin.