Gold and silver are two different things with different value although both get digged out of earth by humans.
However, gold and silver divide the precious metal market. If siver did not exist, many people who invest in it would invest in gold instead, raising its price.
Ditto for altcoins. I don't think anyone would argue that Litecoin, Dogecoin, and other altcoins are stealing investors from Bitcoin. (Most US entrepreneurs, themselves presumably heavily invested in bitcoin, seem to do their best to ignore the existence of those altcoins, or badmouth them whenever they are mentioned, for that reason.)
no altcoin clone (can) have the security of bitcoin.
The existing bitcoin miners could quickly switch to any bitcoin clone that retains the basic PoW algorithm, just by upgrading their software to the appropriate version. They did that after the OP_MUL fork, for example. Again, whether that would happen or not in a future hard fork depends on political factors only.
.@Jorge, The moment is unconducive for learnings. Just let them grieve for now.
Hm, you may be right. Yet, while the price is rising (which it may do again, I have no felling about that) people seem to care even less... When the price is stable and everyone is bored, perhaps...?