There is no "should". Most contract jobs are low risk - they might last for years and if you get fired, you can easily find a new one. Unless there is a major economic downturn, in which case even permanent employees will be downsized.
That's easily worth a 50% salary bump. It also often comes with tax advantages.
In the US 2x or (100%) is the equivalent to a direct hire salary. Since the employer taxes, social contributions, and paperwork filing is directly managed by the contractor now. You’ll have to be your own HR or hire someone to do it for you.
-- you can tax deduct a lot of things, of course, which include day-to-day travel, equipment (phone, internet, laptop), and much more. A part of rent. Let's not even talk about the SEP IRA you can use to further put away money for yourself and lower your tax burden. Unlike an employee 401k, you can decide to put a large chunk of your salary in an IRA at any time, including up until Apr 15 of the following tax year.
-- I'm about to find out, but the lower corporate tax may be a boon here
-- You work 40 hours, or whatever hours. Employees work INFINITE hours. Weekend work, on-call anyone?
I'm not sure what you mean by own HR. For healthcare, you can use the state marketplace or you can look into things like Freelancers Union. For paying tax, you have an accountant. For naughty behavior to report to HR, you have only yourself...
It depends on the market! If people pay 2-3X more, then yes. If you need to be a published author in tech or have previous experience as an MD in an investment bank, then it's a marginal niche market.