Market share is misleading as high speed trains have been deployed on only a few corridors. These are expensive systems that need high volumes - in which case they work. Checking train share of market by corridor gives a better view.
Regarding info from Cato or Reason, I'd take it with caution. They used to produce good research but unfortunately they seem to be driven by ideological choices more than facts. Still a good read but needs fact-checking.
Last - about environmentalists: the overall impact of high speed train depends on how many people ride it. California should be a no brainer as traffic potential is huge. I wouldn't say the same of Spain (where lines are under used).
Overall: don't trust the definitive arguments. Most people have hidden agendas on the high speed rail topic.
From a realistic analysis of facts, you may conclude that California hsr should easily be a commercial success, therefore environmentally good, and has a good chance to be profitable if properly managed/built.
Texas hsr is the same. North east has a great potential but the costs are so high that just a small deviation ends up in huge sums of money in overspent. Guaranteed commercial success but risky from a construction/financial standpoint.
Other projects can be more questionable. I've participated to a review of all them for a potential investor and this is what I remember of it. Don't take it as truth, check the facts.