The Help for Heroes shirt is not political - it's been politicised over the past 24 hours by the extreme right. If we're not careful it will go the same way as the English flag and, if it has to be seen as anything other than the charity shirt it is at the moment, it should be as a way of saying extremists are not going to win in this country.
As for the fact, as LRD points out, the hero rhetoric allows the government to hide their heads because there's a charity supporting injured armed forces personnel, I don't see that it's the 'hero' label that does that. I've helped to raise cash for the hospital that performed my son's heart procedure as the NHS didn't have enough money to supply specialist 'child size' equipment. It's a children's hospital. In Britain. It performs heart operations. And it couldn't afford the right size equipment. Whose responsibility is that? So it's not the hero label that makes the government 'shirk' it's responsibility. If that's the case then we shouldn't have British Heart Foundation, Breast Cancer Awareness, Great Ormond Street etc. cos they are all helping to support people in need. Help For Heroes is a catchy marketing name. Just like using pink as the Breast Cancer Awareness colour is a catchy marketing number. Rightly or wrongly pink is seen as a feminine colour. No one is seriously saying Breast Cancer only applies to women. No one seriously thinks every member of the armed forces is a hero. But...I wouldn't like to do their job, just like I wouldn't like to have to go into a house where blood was seeping under the front door (as a police officer friend of mine had to do a few years ago), nor would I like to have to deal with a violent drunk or drug addicted in A&E. That's why I've never applied for those jobs! My police officer friend often questions why he does the job. Then he has a good day and he understands why. Just like, I imagine, a squaddie questions why he/she does the job when something goes wrong (colleagues or civilians hurt for example), then they see things going right and they understand.
The other thing to remember is that when you sign up for the armed forces, you sign for a number of years. You can't just resign, you can't walk out just because you disagree with a stance or an order. And, yes, I imagine many new recruits sign up thinking it's going to be like Rambo only to discover for them it's more like Apocolypse Now - but many others get a sense of worth and achievement from the good days.
As for the OP question. I asked a Muslim friend of mine, today, if they'd be offended by someone wearing a HFH t-shirt. Their reply was 'no, I'd almost expect it. As long as they were wearing it out of respect for that young soldier and weren't looking at me like I'm the enemy, I have no problem'. As for me. I probably wouldn't have worn it but, as someone once said 'I may not agree with what you say, but I'll defend to the death your right to say it'.