The problem with the web plugin was never its existence. The problem was firstly that it's enabled by default, and secondly that browsers are crap and don't really allow you to enable plugins only for a single domain (yes, there are extensions like NoScript, but it should be "secure by default").
Imagine that if everyone who installs Python suddenly has a browser plugin enabling to run Python code enabled for all sites. I think you will find that Python will quickly become a huge security problem, even though there's nothing wrong with Python as such.