Re: This type of mentality is irrational, bordering stupidity.
The nice thing about plug-in's is that you can uninstall them; with FLASH equivalent functionality in HTML 5, your options to reduce attack surface are somewhat reduced.
Also "Even if Adobe put its top programmers working on Flash, a free piece of software, a lot of people around the world are very keen to find exploitable bugs in the plugin so they can break into victims' computers." can be simply rephrased, replacing FLASH with HMTL5 or whatever. Basically, if a lot of people are going to be using something, then it is going to attract people keen on finding exploits QED.