Some of the things you ask have their answer in the same post you replied to so I recommend that you read through it again, here I'll try to keep it short and simple.
1. People are crossing the mediterranean because their living conditions are bad enough that
they are willing to risk their lives getting to Europe. I'd assume it's not safe where they are if they are willing to gamble with death, and those who choose to make this journey know what they are getting into.
2. Fighting on the side of Assad would probably not have made Europe safer from terrorist attacks. Instead, the population of Syria might have turned to extremist groups for support of their cause. Europe would become their enemy and oppressor, while at the same time being the hypocrite preaching the wonders of freedom and democracy.
3. Refugees get money for the journey by selling what few personal belongings they have left and by putting themselves in debt with the smugglers.
4. We know that refugees contribute to economical growth and employment rates out of experience, these people get less in welfare than they return in taxes and social contributions, such as competition in the labour market and spending in general. Lebanon has registered over a 1.000.000 refugees, and their economy has been growing and is expected to keep doing so. I wrote more on birthrates and why we need refugees from an economical viewpoint on page 14.
5. I don't see anything in that video that contradicts my statement, a few young men are behind this, they are condemned by their religious leaders and police are looking into it. As the expert said, people like these do not pose a threat to the UK.
6. No, you are not removing the blame from them by defining them as radicals,
radical does not mean "to relieve from responsibility". Quoting myself: "Extreme ideas about society are central when talking about radicalization, without these a person can’t be defined as radical." If the people and organizations you mentioned wanted the societies they lived in to change in it's roots, then yes, they were radical and had gone through a radicalization process, if they didn't want society to change in major ways, then no, they weren't radical and had not gone through a radicalization process. Who is a radical depends on what society they live in and how they want to change it, a radical in one society do not have to be a radical in another. Those who proposed equal voting rights for all males were radicals during the 19th century in Europe, but can't be considered radicals today because equal voting rights are now a central part of european democracies. A person can fall for radical ideas during any part of his life.
Agency detection (=presuming purposeful intervention of a sentient or intelligent agent in situations that may or may not involve one) and radicalism are not connected, as explained above, radical ideas take on many forms and shapes but are united in the desire to change society in it's roots, not in the belief of sentient or intelligent agents.
7. Marx did fully believe in his ideas, any historian can confirm this.
8. If you tenfold the the total number of syrian refugees they'll be less than 1% of the european population, but many of these do not even aim for Europe.
If you tenfold the total number of asylym applicants in europe since April 2011 they'll be less than 0,01% of the european population. Europe have some of the richest countries and most well developed economies in the world, we can afford to take these people in, especially if we share the burden.
And it's very basic math actually. Divide something by two and you'll have two smaller sums instead of a big one. You don't have to be very radical to figure that out.
9. To stop thinking would most likely not fix the problem, and neither would thinking, since many people fail the first step: understanding.
This debate is taking up too much of my spare time though so this will be the last post for me in this thread, enjoy yourselves.