Generally, I'm pretty bullish on having both spouses work, especially if one spouse is making significantly less than the other. The additional costs from childcare, taxes, work-related expenses (gas, clothing, having to outsource stuff) often makes the lower-paying job only slightly better than break-even. Leaving the much-higher-paying job, however, definitely has a greater impact.
I think a few points are worth bringing up:
1) You shouldn't care if the stock market crashes while your wife is still working, because you won't be drawing on it--on the contrary, you'll still be contributing.
2) The stock market tends to rebound pretty well after a crash. Big drops don't tend to stick. Even in the wake of the Great Financial Crisis, stock levels returned to pre-GFC levels within 5 years, not 30.
3) I don't know where you live, but $55k of spending for a family of three is probably a lot more than you need. Have you actually run a projected budget if you were to quit?
4) What would happen if you go back to work? You could save an additional...$100k/year. Assuming 5% returns and a 3.5% WR, you'd need about $1.6M. It would take you about five years to get to that point. Keep working and cut your budget to $40k, and you and DW can both retire next year or maybe the year after.
5) The fact that you and DW have discussed this at length, and explored it thoroughly, is a HUGELY good thing.
6) You may be overestimating your tax burden if you quit. $70k - $25k standard deduction = $45k taxable, which gets taxed by $5k, except you have a kid, so it'd be $3k. Sure, add another $5k for FICA and another $2100 for PA state tax, but you're still around $10k total in taxes.
7) You're young, so even if things go south and you get nervous, you can go back to work.