A common word in Japanese, meaning "all-you-can-drink", is "飲み放題". It is "放題" - as much as you would like - appended to the verb-stem of "飲む". It is the same rule for instance, for: 食べ放題, 読み放題, (電話)かけ放題 etc...
Why is it then "やりたい放題" as opposed to "やり放題"?
- A Google search for "やりたい放題" returns 1 790 000 results.
- The same for "やり放題" returns 500 000 results, with the top results being from manicure salons.
やりたい放題
306350,やり放題
53050