@OP - a 2nd referendum is both justified and arguably the only way to settle the issue democratically.
It seems we've had a number of common arguments against a 2nd referendum on this thread, including:
- the 2016 referendum decided the matter, a 2nd referendum doesn't honour that vote and is undemocratic
The 2016 vote was based on a generic leave proposition rather than anything specific. We now have a specific
Withdrawal Agreement provisionally agreed by UK government and EU (although not yet ratified by UK parliament). This is new information for the UK public and another referendum is justified. Also worth noting that having another referendum is intrinsically democratic anyway.
- We don't have time. It's not possible as we're already committed
The EU would very likely grant UK and extension to the A50 period to allow UK to have a 2nd referendum. Even if they don't, then UK can force it by withdrawing A50 unilaterally (as
by ECJ), having 2nd referendum, then resubmitting A50 (EU would grant extension to avoid this).
- the result would be the same. Nobody has changed their mind
There is
reasonable evidence that a small minority would reverse the 2016 decision. Also a strong argument for holding a 2nd referendum - the public may have changed it's mind on this matter.
- having a referendum would damage our negotiating position
The EU have been clear that the Withdrawal Agreement
is not open for renegotiation. If true, then the prospect of another referendum will have no effect.
- A 2nd referendum will increase UK division and will incite far right groups.
The UK is already very divided. Proceeding with Brexit when polls indicate a majority against proceeding will only entrench that division. The UK government or parliament revoking A50 without a referendum will certainly inflame many leavers and it seems likely that a political group (regardless left/right) will gain popularity on the basis that the 2016 referendum was betrayed. A 2nd referendum at least provides a democratic basis for a confirmation of leave or a remain policy. Division will likely continue regardless.
- We just need to get on with it. Let's just leave in March and that'll be it.
The Withdrawal Agreement does not decide the nature of our future relationship with Europe. Brexit will continue to be discussed until the end of the transition period in Dec 2020 at least. If no agreement is reached by then, the NI backstop proposal will be applied and negotiations will continue until the UK & EU agree a mutually acceptable trading/customs position that is consistent with the NI GFA. This situation could continue indefinitely. Even if we leave without a deal, we'll still need to agree our future relationship with the EU. If Brexit proceeds at all, Brexit will continue to dominate UK trade and politics for a number of years. A 2nd referendum with a remain outcome is the only way to resolve the issue quickly.