No. Obviously they wouldn't wait en masse until tax time to sell on the same day. If you knew everyone was going to sell their stock at the same time, wouldn't you sell yours first before the prices started plummeting? And by the same token, if you knew there was going to be a load of selloffs at the end of the tax year, wouldn't you wait to do all your buying at that time?
There's just way too many pressures in both directions for what you claim to be a plausible scenario.
This is so completely irrelevant and grasping at straws that I don't think you're even talking in good faith any more.