TTIP and Brexit

So, I've heard an argument recently that progressives in the UK should vote Leave in the EU referendum because of TTIP. OK. I accept that the referendum debate appears to have placed a moratorium on sanity, but really???

Here is the argument, as I understand it:
1) TTIP as it currently stands is bad. Really really bad. Primarily because it cedes power to US mega corporations, allowing them for instance to sue eu governments if they adopt policies that impact on their profitability.
2) Because of the power imbalance between the EU and the US it looks possible that the US will be able to demand the retention of those sorts of clauses despite opposition from within Europe.
3) By leaving the EU, the UK will avoid having to abide by the terms of ttip.

So, 1 and 2 - no real argument from me, though there is thankfully still some doubt over 2 given opposition from the French amongst others. But please! How can 1 and 2 imply 3? Can anyone seriously argue for a second that although unable to resist the power of US corporations as part of the EU, Britain will be able to do so alone? If a post EU Britain wants to make a bilateral trade deal with the US then it had better prepare itself for a far more draconian set of conditions even than those in TTIP.

Time was that the left were the ones with the truly international commitment to workers' rights. Time was, the left would have stood shoulder to shoulder with European comrades labouring under the yoke of a capitalist, neo-liberal governing elite. Whereas now it seems the hard left brexiters are taking refuge in a self-deluding image of a British socialist utopia that is every bit as parochial and little - englander as that of their UKIP foes.