The problem with radicals isn't that they aren't proposing solutions. The problem is that they are proposing solutions and following those solutions would create huge problems.

One example: We all agree that there too much bureaucracy. Too much useless laws that only complicate things. It takes some insight to understand why the problem exist. Some people without that insight propose that new laws should have expiring dates.

The problem is that those people don't understand what happens in practice. When such an expiry date is reached law gets "reconsidered". The government makes a list with all issues that were with the law in the last years. In an attempt to fix those issues the law then grows by an additional 10-30%. Patching increases complexity and adds new problems.

A lot of the political problems that are raised by radicals are obvious to those people in political power. It might be a valid criticism to say they don't think enough about existential risk. The assumption that they don't think that there's something wrong with the criminal justice system, the economy and the legislative process is mistaken. Seeing the problems is the easy part.

They are too busy with realpolitik. Too focused on the poll numbers of next week. Often they're not smart enough to think of a practical solution.

More generally http://www.ryanholiday.net/their-logic/ is a good blog post on the problem of thinking that you discovered something new.