Too simple. You have entirely forgot about the word investment. Let's imagine the following happened to you PERSONALLY ..
1) You find an investment that will pay a 20% return
2) You find a lender that will lend you any money you want at 10% interest
Do you get into debt or not? How much debt would you get into? Me personally? I'd choose to go MILLIONS into debt and INVEST all the money. What about you? Would you remain debt free to save yourself those huge horrible interest payments? Or would you get yourself 'neck-deep' in debt? You see the problem with dealing just with headlines as dictated by the tories?
YOU are being too simple -- thinking very simplistically 'uh - more debt is bad. Less debt is good. Hoorah!'. First lesson in A-level economics we got told this certainly was not the case. Good headline for the conservatives to spin to Johnny thick public though as they equate government INVESTED debt with their own NON-INVESTED debt from when they bought a plasma telly :/
And of course - no-one knows whether 20 million debt is 'bad and needs sorting', or 20 billion, 20 trillion, 20 squillion or 20 gazillion. So people just believe the hype as what is 'bad' and what is 'ok' is purely (normally misinformed)opinion. The tories say 'er .. the current figure we declare is bad' and we all go 'oooh - apparently x is bad - bad labour - bad ..'.
You are accusing another poster of using too simple economics when yourself are using too simple scenarios as well. Unfortunately it's not as black and white as that the government could borrow, invest and make a bigger rate of retun than its debt interest. When talking about debt there are healthy levels of debt and unhealthy levels of debt, what you suggested is not an axiom to always follow.
To put your example in more realistic terms you need to imagine this:
1) You owe a lot of money to someone
2) Your business expenses are more than its receipts and your net working capital is negative (your liabilities are higher than your current assets)
3) You can borrow, but at an increasing interest rate because your business starts to look riskier every time you borrow more.
4) You can invest what you borrowed at a higher rate of return, BUT, it will take years to see this return, by which time you will need to repay your debt with the income you are generating NOW. By the time your payback period balances, your debt obligations will in all likelihood have spiralled out of control because your credit will be downgraded quickly.
Therefore the option that has the most immediate effect into getting back in the black is cutting your business expenses so that you are no longer bleeding financially. Then borrow at a stable rate (because you have displayed good credit characteristics) and invest so that you can start increasing your revenue. Borrowing when you are deep into debt is not always a good idea. Borrown when your business is making losses is never a cheap option.
When it comes to businesses, a high debt/income ratio (or equally an income loss as in the sense of a deficit) is only acceptable when a business is in its high growth phase, not when its future revenues are expected to be below average (and UKs GDP growth is projects to be below the world average I think, certainly low compared to other emerging economies). Therefore, investing in UK - as if it were a business - would be a bad idea until it debt/income ratio (or profit or income, choose what you will) gets better. As long as it stays high it's simply bad business and there are many good reasons why it's considered like that.