If I make a contribution to a Roth IRA, then later (prior to age 59.5) decide to withdraw some or all of the contribution, not touching the earnings, and without qualifying for any of the exceptions (first home, education, etc.), will I be charged the 10% penalty?

Not if it was a regular (up to $2,000) Roth IRA contribution. You can get a return of your regular contributions tax-free, penalty-free.

However, don't forget about the value of tax-free growth if you leave the money in the Roth. You might be penalizing yourself if you withdraw it without looking at other sources of income first.