Thats not for all alt chains the case, in fact Devcoin is in a legalization process caused by devda.ch. Direct exchange for fiat (swiss bank transfer, sipa, phys. gold and silver etc) is planned for 1. quarter 2013. This means legal cover of a swiss cooperative for devcoin, but means aswell that atacking alt chains is not just a game anymore -  In fact it is a hostile act. Since devda.ch builds on a alt chain, to atack alt chains will be prosecuted by the swiss legal authorities, since it is the equivalent of a atacking the infrastructure of a swiss legal institution. For the atack of a blockchain are two steps needed:

1. You need to dominate the total hashrate of a chain by more then 51%
2. Then You have to follow a certain value transfer pattern, that is causing fraudulent transactions

Just to gain the dominance over a chain, doesnt mean that you attack a chain, or automaticaly do fraudulent transactions. It is not possible to kill a chain as long there is hashingpower. But yes, how you can know when you never dominated a chain.

To say that alt chains are dangerous for btc is simply a expression of not understanding as it is to say to atack an chain is simply done by just dominating it.

Besides all that such activity is disrespectfull to the developers!! It was the opensource developers that brought you not only FPGA early this year as first (no it wasnt BFL) and they now are about to bring you ASIC. So many wonderfull developments was made.. and Bitcoin did strongly profit from that activity as you can see on the actual exchange and hash rate. I remember when BTC was worth like 2 USD a year ago, then FPGA started to rise. Prior to the activity for example there was far less hashpower to secure the btc infrastructure, today we more then doubled the hashspeed. Guys dnt you realy remember wasnt bitcoin 2011 aswell called dead ??

Devcoin is the chain of the Developers, its build protected by cryptochain hardware and software developers (yes BTC developers too), and im sure we will hold against the atacking or even destroying of alt chains. One World one Chain is not the way i see cryptochains working, diversification is the key to stability of crypto.

But this hostile thinking and activity shows me one thing, there could be far more hashpower donated to the altchains. Pool operators why dnt you do something for your miners like offering them merged mining benefit ?? Instead of atacking, you could protect and profit! Attacking a cryptochain is waste of power, and in the long run just expensive and legaly dangerous for the attackers and the pool.