I don't think btc crash is good for alts. All alts will eventually be dragged down if the main coin, btc, that is paired almost every other coin with goes down as well.
That's right, and also don't forget that every other altcoin is "paired" with BTC in most people's minds. And I don't mean crypto enthusiasts or traders, but rather regular people who are only in the process of thinking on investing in this or that coin. Most of those people would abandon the idea of investing in any cryptocurrency if they saw Bitcoin crashed.
This is something that I have been thinking about, if bitcoin crashed and never recovered then it is likely I will not have much faith in this market, at that point what coin could take its place that is not a direct copy of bitcoin, and it is very likely that I am not the only person that thinks in that way so that could spell the destruction of the market of cryptocurrencies.