Well, again, what would that investment be worth if the company bankrupts? Absolutely nothing. A penny tomorrow is better than two pennies never.
There's some element of herding and emotional reaction, possibly. I think there are some justifiable calculations for why an AMD that dilutes shares would see negative price pressure versus one that did not, all else being equal. It's not equal, but I think some of the "positives" can be read more ambiguously.
Depending on an investor's confidence or self-delusion, they may imagine they can time a bankruptcy in some undefined tomorrow versus a surprise devaluation right now.
Even with the simplified 1 penny tomorrow versus 2 pennies never, for an investor it is weighing AMD's one penny of return for X invested weighed against its still non-zero risk of failure and versus "investment Y that could have been chosen instead of AMD". Some risk/return threshold that made AMD the winning choice is potentially negatively impacted by a likely cutting of the return. The idea is that the risk also goes down, but AMD has been polyannish about how everything was turning around before opting to hurt its investors, so they may be justified in asking what risks AMD had to defray or artfully minimized in their disclosures.
Since AMD is a riskier and more volatile investment, it does attract a certain amount of shorter term or speculative investors with their own targets for return. One strategy is the idea that an investor can sucker some other speculator into buying into an even more optimistic risk/reward calculation that AMD has now dashed.
That more positive investor category, and the hedge on counting on selling to that more optimistic investor type, is a source of demand for AMD's stock that would be negatively impacted at the same time the supply of stock rises.
For at least some period of time, a dilution that impacts investors and hinders their ability to meet their goals or offload to others is a valid demerit to AMD's attractiveness.
That it had to be done at all is at the very least cause for scrutiny in case the tea leaves are trying to foretell something more dire than was originally calculated.
The sum of the dilution, hit to certain types of demand, and the specter of it being an indicator that earlier appraisals of AMD's performance were wrong is worth at least a short-term hit.
Longer term, AMD could manage things enough to restore confidence, but it would be laboring under the burden that it's already a poor risk without this occurrence and this would be the 1000th time it's disappointed investors or done something sleazy. Part of the price recovery was predicated on the idea that it wasn't in the position of still having to do this yet again.