The 10% penalty you pay is quite an initial hit and it is worth quite a bit of money in the future. For example, if you have $100,000, you pay $10,000 in penalty. If you are able to compound at 8% annually, that $10,000 has a nominal value of $210,000 in 40 years.
Furthermore, just because you take out the money now and pay the penalty doesn't mean you're exempt from capital gains or dividend taxes.
The above point is actually quite important. Even if you do not do any trading, your dividends will be taxed the year they are paid out. This reduces the compounding effecting on your dividends and it could end up being a large amount of money. Related to trading, if you decide to trade a bit (if you get good enough to know when to sell off if there is a bubble), you will pay capital gains taxes immediately whereas you will not pay the capital gains in a tax-advantage account.
As an example, Let's say you have $100 and any gains are taxed at 20%. For the sake of illustration, let's assume there are two periods during which you make a trade after having doubled your money. If you have a tax-advantaged account, you have $400 at the end of the period and you would lose $80 to taxes upon withdrawal for a net of $320.
On the other hand, if you trade, $100 becomes $200 and you immediately pay 20% which nets you $160. Your second double turns $160 into $320 which, after 20% of $64, gives you $256 net.
You're looking at $320 (IRA) versus $256. And remember, it doesn't have to be a trading situation. If you have dividends, you must pay taxes in an account that's not tax-advantaged. Furthermore, some funds have a large amount of turnover which results in capital gains that are taxed, too.
The only real risk of the tax-advantaged accounts is that Congress passes some law in the future that levies special taxes on tax-advantaged accounts. However, realize that the people with large, tax-advantaged accounts are typically wealthy and have political influence.