Since when is Flash an operating system?
Is that really your best comeback? You used the argument that HTML5 is superior because a whopping 40 companies are working on it, as opposed to one company working on Flash. I then used OS X vs. Linux to illustrate that too many cooks spoil the broth. I could've use the actual food analogy too, but I picked something closer to Flash. OS, plugin, hamburger, doesn't matter.
Anyways here's 10 more reason to avoid the flash plug-in.
1. Take up lots of RAM and CPU horsepower
This could be said about video and games too. Should those be prohibited as well, since the end user apparently can't be trusted to choose for himself whether he wants to use the computer for power hungry tasks or not?
2. Cannot use Google's search/find feature
Wrong. Google has been crawling and indexing Flash pages for over 3 years.
3. Cannot bookmark within the site
Correct, but that's an argument against Flash-based home pages, not Flash content in general (Flash doesn't have to be pages at all).
Yes you can, provided that the webpage has the relevant PHP logic on the server side. If it's lazily implemented, you can't blame Flash for that, blame the designers.
Creating customized right-click menus in Flash has been possible for ages. If developers choose not to implement it, that's their problem.
6. Inconsistent interface from different flash sites
Huh?
7. Not all text can be copied and pasted
Again, that's up to the site designer. Dynamic/selectable text has been possible to do in Flash since, oh lord, at least 2002, probably longer.
8. Cannot link within the site
Huh (again)?
9. Flash on mobile devices arent very stable.
Neither is HTML5, but personally I don't dismiss unstable technologies if they're still in development. Flash for mobile devices is something that's coming later this year. If the final releases are unstable, we can talk.
10. Browsers back and forward button doesnt work
It depends on A) whether the developers have implemented this functionality, and B) whether the browser vendor has added support for it. You can make Flash sites with full back/forward functionality in Firefox and IE, but not Safari (unsure about Opera). I agree that this is a problem, but again, Flash is much more than pages, that's an unwise way to use Flash if you ask me.