Why are you against a country fully regaining its sovereignty and independence? I thought such things were to be encouraged and celebrated. Or that used to be the case at least. Do you also disagree with Canada's independence from the British Empire?
You still don't know yet what kind of Brexit it's going to be.
1. If it's a soft May-style Brexit, you'd more or less have the status quo minus a vote in the EU Parliament, but at least no immediate economic hardship but also no real freedom from EU rules even if the UK would have technically left.
2. If it's WTO rules and you leave it at that, that would just be economic masochism in both the short and long terms.
3. If you're looking at unilateral global free trade in tariffs and quotas and aggressive pursuit of trade agreements to supplement it, you'd still feel pain in the short to medium terms but at least you could rebuild in the long term and maybe come out ahead.
4. Someting else.
If you gave me a choice between remaining in the EU and option 1, I'd definitely vote to remain in the EU. At least the UK would get a vote in the EU Parliament.
If it were a choice between remaining in the EU and option 2, I'd choose to remain because at least the UK would still have free access to the EU market, which would be better than nothing.
If it were a choice between remaining and option 4, I'd still choose to remain because better the devil you know than the devil you don't.
If it were a choice between remain and option 3, then I'd consider it. At least it might bring about long-term benefits, but I'd be under no illusion about it being an easy ride.
Right now, you're just offering a choice between remain and option 4 now that May's deal has been rejected. What kind of choice is that?